gear ratios. should I go 4.10 or 3.73

[Pampas56]

My truck is a 1989 K2500 ECLB (light duty 7600 gvwr/6 lug rims) with 5.7 TBI and 700R4 trans. It will be used for general hauling, light towing (2 to 4K with the RARE 5 to 6K load). 4X4 is for snow and muddy fields, not trails. Maybe some time on Forest service or logging roads.

I bought parts to rebuild the front and rear axles from the lug nuts all the way to the drivelines.

It currently is 4.10, but I bought a 3.73 front diff and gears for the rear axle.

Will 3.73 gears give me better mileage/performance than the 4.10s it has now? I calculate my mileage as 13mpg +/- half a gallon with the RARE high /low tank.

I am not worried about the cost of the parts, they are already bought! Just curious if one is better than the other for my usage.

If some of you folks could give me an idea what your 19' long 4500 lb. truck does with YOUR gear ratios, I would greatly appreciate it.

Also any insights will be read!

Thanks
Steve

[Richard]

Have a 94 C1500 extended cab shortbed purchased new with 3.42 gears. 350 and a 4L60e. Purchased with the high gears because I wanted to lower 6/8 immediately and put 315/35/17 tires on the back, short tire. In stock form when new and stock averaged about 14-15mpg. 17 on long trips downhill. Still averaged about the same after shorter tires. Installed helper bags and frequently used the truck to haul loads when lowered.

About 8-10 years with that, back to stock height (rear still dropped 2" for level). 275/60/17. Pushing 100k now. averaged 13-14mpg.

Wanted something different after 20+ years and lifted the front 5" and rear 2" over stock. Lift spindles, 5/8" coil spacers in front. Stock height leafs in back with 2" lift blocks. Installed 32" all terrain tires. Milage still at 13-14 but trans hunted in and out of OD quite abit under a slight load.
Rear gears went out a while ago. Posted in my build thread about it. I installed 3.73 as replacements. The OD hunting issue is much better and the truck feels to have a bit more performance. The 94 is my DD to this day and milage is still at 13-14mpg with over 180k now.

So, my take is milage will not change much no matter the gears you are considering. Gear the vehicle for the use (load) and comfort level you desire (RPM/sound level) or use most often.

An add- my 2000 GMT400 based C2500 (350 Vortec/4L80e) with a utility bed loaded with tools, rack and almost 300k averages 13-14mpg.

[Palf70Step]

Remeber you'll need to change front and rear gears to match if you want to get rid of the 4.10s. I don't think the MPG would make enough difference to warrant the change. Like richard said, the MPG will be close to the same regardless of what you do, just will you recoop your investment in the difference, not likely.

[Myself]

Not enough info without knowing your tire size......BUT 4x4, 3/4 ton, and towing tell me your probably running a 265/75 16 like stock or maybe even something like a 33x12.50. If so,......stick with the 4.10. A 3.73 will KILL your towing power.

[Richard]

Originally Posted by Myself

Not enough info without knowing your tire size......BUT 4x4, 3/4 ton, and towing tell me your probably running a 265/75 16 like stock or maybe even something like a 33x12.50. If so,......stick with the 4.10. A 3.73 will KILL your towing power.

Not convinced kill is the proper term here. With your 265/75/16 tire example the difference in RPM at 70mph is 200 RPM between 3.73 and 4.10, 1920 vs 2120. Yes the 4.10 will pull a bit harder, but which situation is used more though?
As Palf70step said- is it worth the gear change just to drop a couple hundred RPM for your situation?
Either would be okay for me. I like to shoot for 2000-2200 at my desired drive speed.

[bnorth]

I say leave it 4.10 unless you are doing a lot of highway driving. I am in BC and have spent quite a bit of time in WA so understand what towing is like there. It's not flat like out east.