What happen to my car?When I put the gear on Reverse it is not moving.

What is your question?

My nissan quest runs but only runs to the limit of up to 50mph..if i increase the speed the engine sounds like it's locked,the tire kept squeeking and it is not shifting gears too.I replaced the transmission fluid,the motor mount,also distributor and crankshaft sensor also the tps sensor.I do not know what is the problem now.plse help.thanks