I am considering buying a JD4700 with 1800 hours. I have had a few HST tractors that feel ike they are straining under load. this tractor whines and shutters more then others I am used to. It seems way under power for a 48 HP tractor. The pto power is fine ( I run a pto driven chipper with it). Hills and the york rake really seem to strain it. Is it possible that the fluid is bad? Would a dirty filter cause these symptoms. The tractor is in excellent condition otherwise (It was used on a golf course and appears to be maintained well) Thanks