what gears are better for a 2005 gmc sierra with 285/75/16 tires 3 73 or 4 10?

[p-dog]

I tend to do some towing with the truck and still want to get better gas mileage then 10 mpg on the highway. Don't really want to drop a tire size if i don't have to. Oh ya the engine is the 6.0L. Thanks

 

[Molson02536]

I tend to do some towing with the truck and still want to get better gas mileage then 10 mpg on the highway. Don't really want to drop a tire size if i don't have to. Oh ya the engine is the 6.0L. Thanks

Before you go off and do rear end changes, go to the dealer and give them your vin number to see what rear send you have. You may have the 3:73.1 rear end.

You can also look at your rpo code in the glove box for the rear end ratio you have. Here is a information on gear ratio and tire size.

http://www.drivetrain.com/images/stories/product_imgs_large/gearratiochart_large_large.jpg

http://www.c2e.info/rpocodes/

GQ1 -- AXLE REAR, STD RATIO
GT4 -- AXLE REAR, 3.73 RATIO
GT5 -- AXLE REAR, 4.10 RATIO
GU4 -- AXLE REAR, 3.08 RATIO
GU5 -- AXLE REAR, 3.23 RATIO
GU6 -- AXLE REAR, 3.42 RATIO
G80 -- AXLE REAR, LIMITED SLIP (POSITRACTION)

HC4 -- AXLE REAR, 4.56 RATIO

These numbers can be found in your glove box.example:my truck has a gt4 and g80(limited slip 3.73).just thought some of you would want to know this info.

As for wanting to tow and to keep your gas mileage the same. Just have your ECM reprogrammed to your preference of performance such as shift firmness and shift points. That's dyno tuning and ranges from $150.00 to $350.00 depending on the shop and what's done. You can also see if you can find a transmission shop with a Tech 2 scanner and that can change the transmission's performance such as shift firmness and shift points in relative to your TPS readings as to when your towing.

Not sue which transmission you have in your Sierra, it's going to be the 4L65E or the 4L80E, regardless both have a very low first gear to get the Sierra started and with the 6.0 liter engine, you should be find without rear end swap.