08’ Silverado 5.3 2WD 4l60 trans 165k will start up and run fine for about 5 miles and I will lose all forward and reverse gears. It acts as if it is in neutral (trans temp between 129 and 145 degrees) if I shut the engine down for a few minutes, I can restart the truck and run normally for a few miles. I don’t know the history of the truck before 110k. I haven’t changed or flush the tranny fluid. Any ideas? Something simple or a reman trans is needed.