ok so i'm driving the other day and i pull around a corner straighten out and start to go. engine revs up real high ( goin nowhere) I automatically assumed the clutch went. so i towed it home and put it up in the air. with 1 wheel in the air and the car in gear( clutch out) the wheel spins freely. and i can push the car when its in gear clutch out. i talked to the mechainc and he said that it was either the clutch or the diff. any ideas? PLS PLS PLS HELP