I have a 91.5 cummins with an automatic transmission, it seems like the rpms are going way higher than they should be for it to shift. To get from first to second I have to let of the pedal. Is this normal for these trucks or is something messed up?

 

Adjust your throttle valve cable. Denis Hruza - Dodge CTD - Throttle Lever Adjustment (Kickdown)
You may need to fine tune it from there. I had to slide mine back a little.

 

Is the engine stock or is it turned up a bit?
The stock torque converter is so mushy that if you turn up the power at all, the motor will push thru the converter and hit the governor. Mine did that till I put in the DTT 89 converter. I was told that DOdge put in the junk converter to save the weak tranny from the tork of the cummins.