When accelerating hard the car revs high but doesn't gain speed.

It sounds like a clutch problem to me. If you back off the throttle a little does it grab and go? You could have oil that is on your clutch, i.e. from slave or rear main, or front input on tranny.

When they changed the clutch plate did they adjust the hight of the clutch pedal inside the car.this has a direct effect on the amount of pressure that's applied to the plate due to spring tension.I've worn out two and I'm on my third clutch plate now due to not knowing this and it's a possible reason for slipping trans.