2005 GMC 1500HD 6.0 4X4 Rear end gear question.
 

I have a 2005 GMC 1500HD 6.0 4X4 with 4:10 gears. I'm thinking of changing to 3:73 for the gas mileage. How much of a difference will the 3:73 make. I'm guessing around 300RPM. How much better gas mileage can I expect. I spend most of my time on Freeways.

BTW 33 inch tires and no plan to go any larger.

How much can I expect to pay for gears and install?

figure a grand or more to have it done. if you're running 33's you should have the 4.10's in the first place. going with 3.73's not only may not gain you any fuel milage, but will make it considerably slower.

What he said......... Leave it alone. Your effective gear ratio w/ 33's and 3.73 is gonna be way to tall, if you take the engine out of it's efficiency range RPM wise, you will likely make your milage go down as the motor will be lugging, there is such thing as not enough RPM.

FWIW - My 4.88's are giving me the same overall milage as the 4.10's did w/ 35" tires but, wayyyyyy better towing and acceleration.

33"? stay with 410

Ideal RPM in our trucks for gas mileage is 1800-2000 RPM's. See what your RPM is at cruising speed, and if you're in that range, then you don't need to change anything. If your over or under, though, then change them.

Id say maybe 500 for install and gears. It would be around 1000 if you added a posi as well which if you are back there you might want to think about any way. The G80 that you probably have is not the strongest peice.

around 1900-2000 is probably too low of rpm to turn the 6.0L and still move that much weight around with tires that big.

I hear what you're saying, and of course you may be correct. I've heard, however, that the LS1-based motors are most efficient (fuel-wise) between 1800-2000 RPMs....after that, mileage drops quickly. My recent experience confirms this.

I lost between 2-4 MPG going from 3.73's to 4.10's. My RPMs have gone from 2000-2100 on the freeway to 2300-2400. My truck is no ballet dancer by any means (over 6,000 lbs with me in it), and my heavy 20" wheels and tires, with overall diameter of 32", have been on my truck the whole time.

A big determinant will be cruising speed. Doug90000, what speed do you normally drive at on the freeway? If it's 70 MPH, you may be better off with the 4.10's. If you're driving at 80 MPH most of the time, however, you could benefit from the 3.73's.

Course, we need to know if you do any towing or off-roading....do you need the torque of the 4.10's, or is this truck a freeway driver?

i agree with you there. if you could get your truck to run 2100-2200 on the highway all the time you'd be doing pretty well.

As long as we're picking nits, I'll say 2000-2100 RPMs... :P :devil:


:jest: :jest: :jest:


J/K zippy, your probably right with those big tires.