4l60E Advice needed
If only in forward, try it shifted into [1] or [2] and let us know.
If reverse and forward, then it could be the torque converter, torque converter to flexplate bolts, input shaft or output shaft.
Do you have [P]ark? If yes, then your output shaft and transfer case has to be OK.
Or as you surmise, a failure of the oil pump or even something as silly as the wrong oil filter (e.g. falling into a deep pan.)





