I have recently purchased a Mule 1000. It was only running around 15mph but had spark plugs changed and tuned up but now it runs around 25 mph. The guy that did the work said that he thought the engine needed rebuilding and that I would have to keep changing the spark plugs to keep it performing. I also wanted the gear shift adjusted as you have to wiggle it to get it to crank. he said it was out of linkage. Maybe I should have taken it to the kawasaki place. What do I do about the engine and the gear shifter? can I buy the parts needed to fix the gear shifter? How would I know for sure if the engine was failing?