Chevy Rear End Gear Ratio Chart: RPO Codes & Axle ID Guide

Chevy rear end gear ratios are identified by a three-character RPO code, and GM lists GU5 as 3.23, GU6 as 3.42 and GT4 as 3.73 in its Silverado 1500 option lists for 2019, 2022 and 2025. Your truck’s own code is printed on its Service Parts Identification label, so read the label before you trust a year-based chart. This guide gives the ratios we could confirm in GM documents, the exact places to look on your truck, and what GM says about ratio, towing and fuel use.

What Is a Rear End Gear Ratio?

The rear end gear ratio is how many times the driveshaft turns for each turn of the rear wheels. A 3.42 ratio means the driveshaft turns 3.42 times per wheel turn. A bigger number multiplies engine torque more and keeps the engine at higher rpm at a given road speed, while a smaller number does the opposite.

Chevy Rear End Gear Ratio Chart

This chart holds only what we could read in GM-published documents this session: the Regular Production Option (RPO) code lists in GM’s electrical body builder manuals. Each manual says the vehicle’s RPO list is printed on the Service Parts Identification Label. A blank cell means GM data was not found, and we did not fill it from memory or forums.

RPO code	Rear axle ratio	Model in the GM document	Years in the document	Source
GU5	3.23	Silverado 1500	2019, 2022 and 2025 RPO lists	GM Upfitter body builder manuals
GU6	3.42	Silverado 1500	2019, 2022 and 2025 RPO lists	GM Upfitter body builder manuals
GT4	3.73	Silverado 1500	2019, 2022 and 2025 RPO lists	GM Upfitter body builder manuals
066	4.10	Silverado 4500HD, 5500HD, 6500HD	2019 and 2023 RPO lists	GM Upfitter body builder manuals
005	4.56	Silverado 4500HD, 5500HD, 6500HD	2019 and 2023 RPO lists	GM Upfitter body builder manuals
008	4.88	Silverado 4500HD, 5500HD, 6500HD	2019 and 2023 RPO lists	GM Upfitter body builder manuals
GT5	4.10 is a common claim online	Not confirmed	Not confirmed in GM sources read	None
HC4	4.56 is a common claim online	Not confirmed	Not confirmed in GM sources read	None

Two cautions about reading this chart. First, an RPO list describes options for that model year, so a code on one truck line is not proof of the same ratio on another. Second, the older GU6 and GT4 codes you see on forums matched GM’s 1500 lists here, but codes such as GT5 and HC4 did not appear in any GM list we read, so treat them as unconfirmed until your own label says otherwise.

Ratios GM Listed by Engine in 2005 and 2006

Older trucks are where most searches come from, and GM’s own 2005 and 2006 Special Applications trailering documents (hosted by GM Upfitter) give a useful baseline. Their gross combination weight rating (GCWR) charts show which rear axle ratios appear for each engine with an automatic transmission (the table below is automatic only). They list ratios, not RPO codes, so they cannot tell you what is under your truck.

Model line	Engine	Ratios in GM’s GCWR chart
Silverado and Sierra 15/25/25HD/35/36	4.3L V6	3.23, 3.73
Silverado and Sierra 15/25/25HD/35/36	4.8L V8	3.23, 3.42, 3.73, 4.10
Silverado and Sierra 15/25/25HD/35/36	5.3L V8	3.23, 3.42, 3.73, 4.10
Silverado and Sierra 15/25/25HD/35/36	6.0L V8 gas	3.73, 4.10
Silverado and Sierra 15/25/25HD/35/36	8.1L V8 gas	3.73, 4.10
Silverado and Sierra 15/25/25HD/35/36	6.6L V8 turbo diesel	3.73
Tahoe, Suburban, Yukon, Yukon XL	4.8L V8 and 5.3L V8	3.23, 3.42, 3.73, 4.10
Tahoe, Suburban, Yukon, Yukon XL	6.0L V8 and 8.1L V8	3.73, 4.10
TrailBlazer and Envoy	4.2L L6	3.42, 3.73, 4.10
TrailBlazer and Envoy	5.3L V8	3.42, 3.73

The pattern is the useful part: the small V6 and V8 engines were offered with the lowest numbers, and the 6.0L, 8.1L and diesel engines started at 3.73. The 2006 document shows the same ratios for the 4.3L, 4.8L and 5.3L pickups and for the Tahoe and Suburban 4.8L, 5.3L, 6.0L and 8.1L rows. A ratio appearing here means GM listed it for that engine, not that every truck had it, and 2003-era trucks are not covered by these two documents.

Ratios in GM’s 2024 Trailering Guide

For a current comparison, the 2024 Chevrolet Trailering Guide publishes an axle ratio beside each engine in its weight tables. In several of its tables a single ratio is listed per engine.

Model	Engine	Axle ratio in the guide
Tahoe and Suburban	5.3L V8, 6.2L V8 and 3.0L Duramax	3.23
Silverado 1500 box delete	5.3L V8	3.23 (GCWR 15,000 lb)
Silverado 2500HD and 3500HD box delete	6.6L gas V8	3.73
Silverado 2500HD and 3500HD box delete	Duramax 6.6L V8	3.42
Colorado	2.7L Turbo 4-cylinder and TurboMax	3.42
Express passenger and cargo vans	4.3L V6 and 6.6L V8	3.42

Source: 2024 Chevrolet Trailering Guide (Chevrolet). The guide covers the model year it is written for, so do not apply these ratios to older trucks.

How to Find Your Chevy Gear Ratio

Start with the paperwork on the truck itself. These are the places GM documents point to, in the order we would check them.

Where to look	What GM documents say	How to use it
Service Parts Identification label	GM says the vehicle’s RPO list is printed on it. In the 2024 Silverado 1500 manual, a large barcode on the certification label on the center pillar can be scanned for the VIN, model designation, paint information and production options. If there is no large barcode, the same information is on a label inside the glove box.	Find the 3-character code that matches the chart above, such as GU6.
Trailering Information Label	On the driver-side door jamb of Silverado 1500, Silverado HD, Suburban and Tahoe in the 2024 guide. GM lists GVWR, GCWR, rear GAWR, maximum payload, maximum tongue weight and curb weight on it.	It carries weight limits, not a ratio, so use it for safety numbers after you know your ratio.
Window sticker or build sheet	Not described in the GM documents we read.	Not confirmed in GM sources read.
Axle tag or counting turns	Not described in the GM documents we read. Counting driveshaft turns per wheel turn is an arithmetic check that needs the rear wheels raised.	Not confirmed in GM sources read. We do not give lifting steps here.

The label wording above comes from the 2024 Silverado 1500 owner’s manual, so an older truck may place the label differently. If your manual shows a different location, follow your manual.

How Do I Know What Gear Ratio My Chevy Rear End Is?

Read the RPO list on the Service Parts Identification label, then match the three-character code against GM data for your model and year. On Silverado 1500 option lists, GU5, GU6 and GT4 stand for 3.23, 3.42 and 3.73. If your code is not in GM data you can read, do not guess the ratio from a forum chart.

10-Bolt vs. 12-Bolt vs. 14-Bolt: Which Rear End Do You Have?

The bolt count usually refers to the number of bolts around the differential cover, and it describes the axle housing, not the ratio. The GM documents we read give ratios by RPO code and by engine, but they do not list axle bolt counts by model, so we are not publishing a bolt-count-by-year table. Two axles with the same bolt count can carry different ratios, and one ratio can be sold on more than one axle, so the bolt count never replaces reading the RPO code. Axle strength and gear sets are specific to the housing, which is a good reason to confirm both with a dealer parts counter before ordering gears.

Gear Ratio, Towing and Fuel Economy: What GM Says

GM states the general rule plainly in its trailering guide: a higher axle ratio offers higher trailer weight ratings, quicker acceleration and less fuel efficiency, while a lower ratio offers more fuel efficiency and quieter operation but slower acceleration and lower trailer weight ratings. That is the whole GM statement. It does not give a mpg figure per ratio, so we do not either.

The more useful correction is that ratio is only one input. GM says the maximum trailer weight rating is not specific to an individual vehicle and is most useful for comparing product lines. It assumes a driver, a front-seat passenger and required trailering equipment, so extra passengers and cargo cut the weight you can pull. GM also says the only way to be sure you are within the ratings is to weigh the loaded tow vehicle and trailer.

For conventional trailers GM puts tongue weight at 10% to 15% of loaded trailer weight, and for gooseneck or fifth-wheel trailers it puts kingpin weight at 15% to 25%. Neither number may push the truck past its rear axle or vehicle weight rating.

Safety Limits Before You Tow or Change Gears

• Never exceed GVWR, rear GAWR, GCWR or the trailer weight rating. GM says the combination must stay within every one of them, and that the GCWR is the total allowed weight of the loaded vehicle plus trailer.
• Read the weight limits from the label on your own truck, not from a chart for a different year. The 2024 guide says the Trailering Information Label is on the driver-side door jamb on the trucks it covers.
• Use the towing guide for your model year. Ratings in the 2024 guide apply to 2024 trucks and should not be moved onto a 2005 truck.
• Do not work under a raised vehicle supported only by a jack. Follow your owner’s manual for lifting and support, or have a shop do it.
• Changing the ring and pinion changes how the truck drives and can affect warranty and weight ratings. Ask a GM dealer or a qualified driveline shop before you change ratios, and keep any ratings from the original label in mind.

Model and Year Searches We Could Not Confirm

Searchers ask about specific trucks, and we would rather say what GM data we lack than guess. This is where each common request stands after reading the GM documents above.

Search	Status
1998 pickup, 4WD	Not confirmed in GM sources read (GM 2005 and 2006 documents start later)
2003 Tahoe or Suburban	Ratios by engine appear in GM’s 2005 and 2006 charts only; a 2003 truck’s own code is not confirmed
2007 Silverado 2500	Not confirmed in GM sources read
2012 Suburban 1500	Not confirmed in GM sources read; GM’s 2024 guide does not apply
1980s and 1970s trucks, 1948 Chevrolet	Not confirmed in GM sources read
Chevette and other small cars	Not confirmed in GM sources read

For any of these, ask a GM dealer parts department to read the RPO list for your VIN, then compare it with the codes in the chart. A related read on our site is which drivetrain suits towing, and for axle versus driveshaft problems see driveshaft vs axle failures.

Keep reading

• Ford 8.8 vs 9 Inch Differential: Strength Compared
• Chevy 6.6 Gas MPG: No EPA Rating, Real Test Numbers
• Chevy Engine Swap Compatibility Chart: SBC, BBC & LS Fit

Frequently Asked Questions

How Do I Know My Chevy Gear Ratio?

Read the RPO codes on the Service Parts Identification label (the 2024 Silverado 1500 manual says it is on the center pillar certification label barcode or on a label in the glove box) and match the axle ratio code to GM data for your model year. GU5, GU6 and GT4 are 3.23, 3.42 and 3.73 on Silverado 1500 lists.

How Do I Identify My Chevy Rear Differential?

The GM documents we read identify ratios, not housings. Use the RPO list on the label, then have a dealer parts department confirm the axle from your VIN. We could not confirm a housing by year from GM sources.

Is 3.42 Or 3.23 Better For Towing?

GM says a higher axle ratio generally offers higher trailer weight ratings, so 3.42 generally rates higher than 3.23 on the same truck, at some cost in fuel economy. Your truck’s own weight ratings and trailer weight still decide what you can pull, so check the label and the towing guide for your year.

What Is the Most Common Chevy 10-Bolt Gear Ratio?

We could not confirm this from GM sources. GM’s lists show which ratios were offered, not how many were sold. Check your own RPO code instead of assuming the most common ratio.

How Do You Identify a 10-Bolt vs. 12-Bolt vs. 14-Bolt Rear End?

The bolt count refers to the differential cover bolts on the axle housing, and it does not tell you the ratio. The GM documents we read do not list bolt counts by model, so confirm the axle by part number with a dealer before buying gears.

What Does GU6 Mean on a Chevy?

GU6 is the RPO code GM lists for a 3.42 rear axle ratio in its Silverado 1500 option lists for 2019, 2022 and 2025. A code from another truck line should be checked against that line’s own GM list.

Conclusion

Read the RPO list on the Service Parts Identification label, match it to a GM source for your model year, and keep every weight limit from the label on your own truck. Where GM data is missing, ask a dealer to read your VIN.