Any oil in the oil sump? Are the revs under 6,500 rpm? Gov-na' disabled to make it a racing mower? Do any mud bogging? Deck removed creating an ATV?
Oh, in DRIVE. Look at your drive belt/s and any idler pulleys. Bearings okay? Any round hay bails up under there? Take pictures of everything and post up in here. Socket wrench left on top of the transmission now stuck in the drive belt?
slomo