I have some problems with my T680

I know the truck very well and the Cummings transmission is a step up for exactly what you're talking about. What you have IMO based on my
history with this unit overall is an electrical/computer malfunction between the PACCAR Tmission and the brain aka software aka CPU.
Here are some beginner things to check off... Power off the unit most units have the power off or kill switches down below by the seat belt near the base of the driver side door. Make sure your fuse box and fuses are normal. Check as best you can for any loose or faulty (female to male) wiring. If the kill switch doesn't fix or clear the error or issue you are having. There are some key/ignition turns or codes you may try for starters. Lastly, if you have a friend or you know how to plug into the truck with the proper KW software and a lap top do that. Some places charge out of the arse to do this alone and smile right in your face when you come to pick up the unit. Like they put in hours of work. I am just trying to help if some KW shop professional knows more than me you will be better off. I don't want to make your problem worse or be trolled because I am not spot on like a pro mechanic! I hope something helps or rings the bell so to speak LOL!! cheers Driver GL!!!