The last couple of times to the dunes I have experienced a severe power loss in my XTZ. After bring it to the dealer they said it was the belt slipping. I replaced the belt and still no improvement. In fact it is getting worse. Only able to get up to 45mph on flat desert. I was getting beat up the hill and on the flats by RZR's, Teryx's, and even a few Rhino's. Any suggestions?