The top ones run a bit more hot than the bottom bearings, shoot a temp gun at them and see what you got. As far as the slow grinding I would say sharpen or put new teeth.I got the machine a couple of months ago. Put about 60 hrs on it so far. I grease bearings every couple of hours. 2 or 3 shots. I ground a stump today, took about 2 hours, 5 ft. Diameter lychee tree. After about 15 minutes I checked the cutter wheel bearings and the two bearings above those ( jack shaft bearings?). The were fine to touch, not to hot. When I was done with the stump they were Hot. Guess its time to change them or is that normal after 2 hours of operation?