What would cause a 4l65e transmission to, while traveling down the highway, all of a sudden jump out of drive? 1st gear is great, 2nd gear starts good, but then it starts a grinding noise until my speed reaches 25-30. Then the grinding noise stops as I shift into 3rd gear at 40 mph. It drives fine until I go back down to 40, then it slips out of gear. There is no 4th (drive) at all; I can only manually shift.
It sounds to me like you have some internal problems with your transmission, and it will probably need to be disassembled to find the cause.
Updated on April 3, 2018
By Eddie Carrara