New to the Cummings world. Driving at about 1500 rpm at about 55-60 MPH and the rpms will jump. Almost sound like it is trying to downshift. Any ideas?

 

first thing to check is make sure battery cable connections are clean and tight.... that is taking them off and cleaning the connection even if they look clean to the eye... this can cause voltage spikes in the system allowing the computer to think torque converter clutch needs to be engaged and disengaged.... worse case could possibly have a torque converter clutch getting weak another possibility is a falty pedal position sensor best diagnosed with a scanner to monitor voltage from it

 

Cleaned posts on both batteries. Ran for about 25 miles on cruise at about 60 (1600rpm) not even a hiccup. Thanks.

 

Ya that just hapend to mine I needed new batt cables for the fix you are lucky you found it that quick mine was just start replacing and hope!