2012 ProStar Automatic Transmission Issue

I have a 2012 Prostar( Maxxforce 13, Eaton Fuller Ultrashift plus) that is giving me problems. Runs fine for an hour or so, then loses all pulling power. Problem started a couple days after the driver got stuck in sand and had to be pulled out. There are 2 active codes, that seem to involve the headlight interrupt switch and another that I have been told has something to do with the SART module. Only thing that changes when the truck loses power is this...Truck starts off in 2nd when running correctly, once it loses power it starts off in 1st and seems to hit higher rpm's before shifting. It will get up to 55 mph, but gets wiped out by slight hills. Was hoping for a little help before I have to give my first born to the dealer.

 

No, I haven't tried that. How would I turn it off?

 

Truck starts in 2nd gear when running correctly. Once it warms up it loses pulling power and
starts in 1st gear after coming to a stop. The engine sounds the same as the other 5 units I have.

 

Any ideas/opinions are greatly appreciated.