F350 With Strange Noise While Towing.

I ran into this in Mexico. A gringo Ford pickup was thumping. After trial and error we finally got it to finally kick into neutral and coast to a stop regardless where the transmission manual valve was selected. Put it in reverse and the truck backed up like normal and all forward gears worked normally again. Not satisfied with that we but the vehicle on jackstands and then further lifted the front or the rear. This made the problem worse with the front end higher. The owner had the truck towed 3oo miles, The Ford Dealer said the ECU had stored no fault codes. He ordered a four thousand dollar transmission from the states. I do not know the outcome.

You need a hotshot Ford automatic transmission specialist's diagnosis if your rig has an automatic transmission. I can offer nothing if it is a manual trans.