i want to change the rear end from 3.53:1 to anything higher, will this make a mileage difference??????

 

First, unless there was a custom something or other done, you have 3.55 gears, not 3.53. The only gear ratio options were 3.21 (IIRC), 3.55, 3.92, or 4.10 from the factory for 1500s.

Hopefully you have a 4x2, otherwise you'll want to change both axles' gear ratios. Rear axle only equals about $400 in labor roughly, both equal about $800-$1000 (front Dana 44 is harder to do then the rear).

The mileage difference depends on your tire size. If you have larger than factory tires, it may actually go up in MPGs. Factory tires, it'll go down.

I'll move this to the 2nd gen section (1994-2001 1500s) for you.

 

Have you changed the plenum? when was last tune up? how the CAT? O2sensors? Does it have the 'Deathflash"?

All these are huge impacts with mpgs



i have 4.10 gears with 265/75/16 10 ply tires(heavy)....and last summer i was getting 13-14 city mpgs, with 17-19 on highway.....this winter, it went down a bit, but it happens....but i did a 218 mile trip on the highway and i used left then half tank of gas and i have a 26 gallon tank...in the winter my city mpgs deplete to about 8-10...but my highway mpgs are still high. and my truck is the 5.9 with 207K...but lots of $$$$ invested....

 

Check plenum, give it a tune up. Maybe upgrade a few things to help it breath better.