?Gear? ratio for 2010 GMC Sierra crew cab

Please take a read of this thread for my opinion of 3.08 vs. 3.42 with 6-spd trans. I say stick with what you have. Limit yourself to 4th gear and use tow/haul mode.

The good news is that you have the six speed transmission that will give you a towing gear, either 3rd, 4th, maybe 5th, that will put your engine in a good rpm range for towing your trailer regardless of the rear axle ratio. The diesel guys will now tell you how they tow in 6th. We, who have gasoline powered tow vehicles, generally don't.

Sounds like you have the 3.08 gears!

The gear ratio has to do with how much power your truck will have in pulling heavy loads. With a higher number (4.10 vs 3.55 for instance)You give up a little gas mileage (when not towing) but increase it's ability to pull loads better when under stress such as up steep hills, in the mountains, getting it started from a stop at a light, etc. You also will get slightly better mileage when towing because the engine will not have to run at as high a RPM. Lower gear ratio's 3.08, 3.42 get better mileage and have less power than higher 3.55, 3.73, 4.10 ratios when not towing. Opposite is true when towing (usually).

Most people that tow heavier trailers want one of the top two (3.73 or 4.10) for a chevy. 3.04 is going to get nice mileage when not towing but your going to be using the debit card when you are. Gonna work it hard going up hills but it will pull that trailer, just going to be screaming (high RPM's) going up hills.

I have a crew cab 4x4 with the same engine and the 3.55 gears and it runs about 4500-5200 rpms up Jellico mountain pass in Tenn. It maintained speed but sounded like it was going to jump out from under the hood.

Thanks for all the help!!! Our label has GU4 (which I assume is NOT the best) but it also has G80 AND the Z82.

Can someone explain in baby steps what on earth I am asking?

We have taken about 5 trips so far this year, nothing more than 2 hours away, and had no trouble so far. In the long run, after about 1 more year, we plan to do the whole "out west" thing and we are sure hoping this set-up will work.

As stated previously, our trailer dry weight is 5400 pounds.

I have quickly found that the "help" on this site is much more knowledgeable than the ones working at the dealership, although, it may not be their fault. It was a used GMC sitting at a Subaru dealership..... :) :)

PA12DRVR wrote:
to wmoses

I changed my axle ratio on a 2002 (?) 2500 Suburban from 3.73 to 4.10. Made a noticable difference towing a circa 8,000# TT.

Hurt my unloaded gas mileage a bit, but since the primary purpose of the vehicle was a tow vehicle, it was a good tradeoff. I was close to out of warranty in any case, but asked the dealer about it and they told me they would not warranty the new gearing, but that the change would not void any other part of the powertrain.

i'm surprised it hurt your gas milage a bit... unless i'm missing connotation and you intend to mean a little bit and not quite a bit. we swaped the whole rear end in my mothers suburban which included the same gear change and she only lost 1-2 mpg... maybe the shift points in the tranny needed to be corrected?

i changed mine (3.55's to 4.10's) because of bigger tires (35's) and i was able to get pretty close to my stock mileage and my speedo is back to being accurate (comparing it to my gps)

Side note: changing gearing maybe the limiting factor of tow capacity but i'd be careful when assuming that you've increased it with a gear change.

to wmoses

I changed my axle ratio on a 2002 (?) 2500 Suburban from 3.73 to 4.10. Made a noticable difference towing a circa 8,000# TT.

Hurt my unloaded gas mileage a bit, but since the primary purpose of the vehicle was a tow vehicle, it was a good tradeoff. I was close to out of warranty in any case, but asked the dealer about it and they told me they would not warranty the new gearing, but that the change would not void any other part of the powertrain.

Look in the glove box for this sticker with list of RPOs for your truck.


You wither have GU4 (3.08) or GU6 (3.42). Also, G80 is the Eaton locking rear differential, a very good performance improving feature.

More importantly, you will want to verify you have Z82 for HD trailing package.

While we wait for the OP to come back and say that she found her axle ratio from all the help above, I'd like to ask ....

Has anyone changed their rear end gears to increase their towing capacity?

I asked my dealer for a quote which they gave, but said that doing this will void my power train warranty - even if they did it!

I have a 2007 and my trailer is also 5400 unloaded and it tows great. I also only have the 4spd tranny with 3.73. So with the 6spd and most likely the 3.42 you should be good to go. Key is to not load the truck bed much as you will run out of payload quick.