So what kind of RPMS and MPH are you all runnin at cruising speeds on the highway? I am cruising at around 75 MPH and runnin about 2500 RPM. Just wondering if thats how everyone else is runnin.

 

Your right on the money for the 4:10 gear. Dont worry about the Cummins,it likes it!!!.I keep mine pegged all nite towing a 27ft trailer and Ive got 90k on it. It runs better now than it did when it was new. 2004 6spd 4:10gear Bone stock.

 

2100 RPM's @ 75mph

 

1950 or so rpm doin 70mph. noticed a drop in rpms when installed the wastegate and intake mani.

 

Agree with Melon. Your right where I am with 4.10s. I'm usually getting 18-19 hwy and 15-16 city.

 

Yup! With 3.73's at 72 MPH, I'm turning 2K.

 

actualy he's got 3.73's. . . .what your seeing is the higher final drive ratio of the g56 trans. . .my NV5600 with 4.10's is the same as your truck. . .if I had 3.73's I would be closer to 2K at 70mph. . .it's high, but if your easy with the skinny pedal on the right you can get some good fuel mileage

 

I have a 1990 CTD that I just put togeather with5 speed and 3:07 gears, it runs 1550 @ 65in 5th
4th is good for 77 and 5th is good to 106, & my son verified this reciently at 105mph. I coulda killed em!!
I loved that truck, now I drive a 1999 P-pumped CTD

 

Yep, your running the 3.73 gears and the G56 tranny. Mine does the same. At 65 you'll get great mileage, at 70 not so good, at 75+ it sucks. The good thing is, this set up loves to tow. My camper does not slow me down on the interstate.

 

I'm getting pretty decent fuel milage. I have bumped up my speed to almost 80 and im getting 18 mpg.