Hi guys. I am having a problem with my x748. If I attempt to mow long grass (7 iron deck), the PTO shaft will slow to a stop. Once out of the long grass the PTO will spool up again. Seems to be load related. The greater the load, the quicker the PTO shaft will stop spinning. The PTO light on the dash stays illuminated the entire time. Belt has been replaced on deck, belt tensioner is fine, blades spin freely. Any ideas? PTO clutch?