Hi there, I have a JD D100 tractor, bought last year.. we don't use it much so it sits a lot. I noticed that we're having a problem with the blade speed. If the blade height is 1 or 2, the blades barely spin at all. Up at 4, they seem to spin fine. If I start the blades at 4 inches, they're fine, but as I then lower it, the blades slow down, til I think they're not spinning at all. What do I need to adjust to get things working again? The little LED on the tractor says 8.2 , if that helps..