Transmission issue

[Mezz519]

Hello everyone, and thank you Rawze for the invite.

2017 Peterbilt 579 with 16 speed automatic eaton. ISX15.
Recently I started having a very random issue with my Pete.
It started at a truck stop in the fuel isle. I came to a stop and put my tranny into neutral and set my brakes like I always do. After fueling I go to start my truck and the transmission gear select box shows service light flashing and on dash showing N for neutral then switching to F. Back and forth. After a few attempts it started.

It didn’t do it again for a while. Then at the booth at the border in Detroit/Windsor it did it again. I almost got towed but last minute got it started.

Then on my way back into USA again at the booth same thing happened. Officer gave me 25 minutes to get it started and it just wouldn’t start. Constantly flashing service and showing F/N on dash where the gear number usually is.
This time the tow did come and towed me out costing me 1400 USD. While out of the booth the truck started.

Has anyone had this issue before and where should I start diagnostics. Friend of mine said the harness would be a good start but with so many things possibly affecting it I was wondering if someone here had a better idea.

Thanks in advance.