My 96 C.T.Diesel 's runnin' like s***. It accelerates and decelerates with no problems, yet when I'm coasting or cruizin' at the same speed, it's upshifting and downshifting erratically without throttle change. Would the TPS be faulty? Is is a fuel pump problem? I thought it was happening with just the trailer attached, but it's doin' the same with/without the trailer. It starts well, and if you mash on the gas it'll get goin' , it's only when I'm cruizin' on the highway. Idle's fine. Let me know what you think.

 

If it is just doing it with the torque converter locking and unlocking then it is probably just a bad / dirty TPS sensor. https://www.dieseltruckresource.com/...threadid=42649