I know by researching on here that most people go from 3.23s to 4.11s. Well, I probably would go 3.90s if I didn't already have a GM set of 3.73s that cam out of my 1990 truck. The question is, what should I expect as far as mpg, probably decrease on the hwy about one mpg but city will probably go up as the truck is not struggling to get off the line as much. This is not my race truck, just a daily driver that I need a bit more towing from and performance. And since I already have the 3.73s and all I need is a install kit, then figured can't really beat that performance gain either way.

So, what are y'alls thoughts?

The truck is a 2007 Classic Crew cab 5.3L with SS 20" wheels on 285/50R20 tires. Probably will be going down do a 275/45R20 or 265/50R20 in a year when I do a 2/4 drop.

 

I went from 3.23 to 3.73s in my truck. The difference was pretty dramatic on the highway and stop and go traffic. I could go 500 miles to a tank before the swap at 80 mph straight highway. Now I get 420 on a good day at the same speed. Stop and go traffic took a lot less effort and didn't quite stall up as much but, the gas mileage just about stayed the same.

 

Wish I could get 400/500 miles to a tank in my 4.8 crew cab with 3.23's... Im only getting around 240ish..I do,do alot of stop and go though..

 

My crewcab performed pretty well with 3.73's but I couldn't really compare to the 3.23, for they were already in the truck lol.

 

Right now, I average about 320-330 miles per 17-18 gallons of fuel so about 18.5 - 19 mpg.

 

Anybody else have input?

I know its going to perform better and feel better just driving it around. Most of my driving is 50-65mph.

 

I just went from 3.42 to 3.90 and the difference is noticeable, both in cruising speed rpm and ease of acceleration. Haven't hammered on it yet. However, in the short time (100 miles) they have been in, I have seen about 1mpg better in town.

 

I don't think the gear from a 90 model will work

 

They will. I used some from a 94

 

My input not good enough for you