Allison transmission

I had to drain all the trans fluid when I changed that sensor because it was on the valve body inside transmission. I just done a full service and put both filters on it and new fluid. Fluid level is right on the money. I dont have any other symptoms of a bad tcm. I was thinking wiring also. About a month ago I had headgaskets and studs put on and they had to remove the cab and it wasn't long after i got it back i started having this issue so im wondering if its something they unhooked. Just don't know were to start really

I'm not sure on the reflashing part. I have a edge monitor on the truck. I changed one of the things to read the transmission temp were i could compare it to the stock gauge. When it does its thing and the stock gauge quits it send the temp straight to 170 on my monitor. Like for example if I start the truck and let it run and start down the road and my stock gauge is reading 120 on the temp and I make a left hand turn and the gauge bottoms outs my monitor instantly goes to 170 on temp

Okay I'll try that. And I'll try to get in touch with the guy that done the headgaskets. Thanks for all the help