I BEING TOLD THAT MY TRANSMISSION BURN IT WAS RUNING PERFECTLY AND SUDLENLY I WASNT ABLE TO SPEED MORE THAN 20MPH BUT STILL RUNS IM NOT SURE IF IS TRUTH SINCE FIRTS THEY SAID ALL I NEED TO DO WAS A TUNE UP FOR IT
If one of your auto transmission clutches is burnt, then the clutch will not be working, therefore at least one of your 'gears' will not work. A symptom would be that your engine would rev high, but you wouldn't be able to go any faster. Being limited to 20 MPH certainly sounds like a it could be a burnt clutch. @Robert S. Barnes is correct that the transmission fluid will also be dirty with clutch lining.