3.42 gear ratio

My truck has 3.73 with 11r 22.5 tires and a 10 spd. I run 65mph no problem. Over 6.5 mpg pulling a flatbed with a Cummins ISX.

 

New trucks are programmed to run low rpm older engines like to sing a bit more.. mixing the two rarely works .. talk to Detroit Cummins etc and ask where a certain model year engine should be run for fuel mileage or performance depending on what your after

 

Why wouldn't it be? 80k is 80k van or flat. It'll be fine

 

There’s not a big difference between 3.42 and 3.55, not enough to warrant a gear swap. Your truck sounds laggy. Or has a boost leak. Or she can’t breathe (when is the last time you checked the breather filter?)

If you’re going to swap gears, 3.55s would be a waste. You’d have to do 3.70s or better.

 

The question is what do you want.
Lower RPM at speed. Then go taller.
Higher RPM at speed. The go short

Tall gears 3:24, 3:36, 3:42, 3:55, 3:70, 3:90 short gears
Lower RPM to Higher RPM

 

Transmission Ratio RPM Calculator | Spicer Parts

Lp22.5 is 40"
11r22.5/lp24.5 is 42"
11r24.5 is 44"

 

No, truck/motor is fine, I just through a number out there and my desire to swap out the gears. If I do, I would more than likely look at something in the 3:70 area. My best truck, doing this same kind of work, was an old Volvo running 3:90 gears. That may be a little much for this particular truck, but 3:70ish would be night and day running local/regional as would 3:58's. The big question is fuel mileage and the ability to keep everything in synch, RPM vs Road Speed. When I get serious about doing it I will need to sit down and do some figuring. Not something I am just going to go do on a whim. Oh, those are pretty, throw them in, ain't going to happen.

 

You said...

A factory 600 described as a dog? That truck should have enough power to change the rotation of earth. Even with those gears you have. Do you have a boost gauge?

 

The motor is fine, it pulls like a freight train... Not the issue, stop lights, traffic, etc are the reason I want to swap out the gears. I run local/regional, Michigan, Detroit, Flint, Lansing, Saginaw... If OTR, no issue with the gears.