98 9400 w/n-14

Did those other shops have a computer to diagnose or just taking a guess?

 

I agree, need to find what codes are active first. You can spend a lot of time and money in a hurry. If it pulls good to 1600 and then just stops pulling and it is 1600 everytime, I would suspect a faulty throttle position sensor or speed sensor. Coolant sensor, intake sensors all can give bad readings with no check engine light, but I have never seen one malfunction at same rpm. The throttle pedal gets wear and presents with a dead spot in the pedal. Speed sensor possible, I would pull it and clean it and try again.

 

I suggest you take it to Cummins and have them put it on the dyno hook the lap top up to it and run it until it gets hot and see if you can duplicate the problem. Otherwise, hook a laptop up to the truck and drive it until the problem occurs and see what it going on.