what gears?

[old man dave]

Have you verified your speedometer with a GPS or recalibrated it? The 37s could be giving you a false speed/RPM ratio now.

 

[backwoodsboy]

OP, you've got something strange going on. Either a) you don't have 3.55's b) you aren't running a true 37" tire c) your speedo is out of calibration, and you're travelling a whole lot faster than you think.
At 70mph, with a true 37" tire and 3.55's you will be turning 1700rpm.
At 70mph, with a true 37" tire and 4.11's you will be turning 2000rpm.
With a true 37" tire and 3.55's you will be running 81mph at 2000rpm.

Pick your poison.

 

[97strokerHD]

I still need to check what gears I have by rotating tire and checking driveshaft revolutions. The speedo could very well be off. I have to use a scanner to calibrate that right? Also what is the normal "sweet spot" rpm for highway crising with these trucks?

 

[idshred]

There is a procedure to recalibrate the Speedo. Google 'obs speedometer recalibration'

it's not too hard to do.

 

[gnxtc2]

I have 35's with 3.55's. It is great empty, but a bit high geared with a load.

Just increase HP.....problem solved oke:

Billy T.
[email protected]

 

[Garbage_Mechanic]

Just increase HP.....problem solved oke:

Billy T.
[email protected]

I like your thinking Billy. I wouldn't get away with it at all without the performance mods I have. The problem is low speed maneuvering of a loaded truck or truck / trailer. Fortunatly is easy to use low range to fix the problem. I have had more clutch chatter since I put the Valair in place of the failed South Bend.