7 shops 10k still broken

If the DEF gauge blinks red, that usually indicates the engine has locked into a Government code (code set when after treatment codes are ignored) by the 5mph restriction isn’t supposed to set until it see’s either a rise in your fuel tank level or def tank level.
It will act funny but it shuts off fuel above idle at 5mph no matter the engine speed. But the dealer should have seen that code. Was the glue stuff you found in the harness; was that the new or old sensor harness (larger 120 pin connector)? Or the oem side harness ( smaller 21pin connector)

 

T P S is a cheap fix that just plugs in under fuel pedal and can act like part of what you are feeling while trying to pull a loaded trailer?