I have a 14 speed 7 high & low. I put new drive belts on it & it still slips going up even small inclines. I have been going up these inclines & had it stop. I smelled rubber. I got off & looked, & saw the engine side belt slipping on the engine pully. I got my belts from a reputable guy, but there not mtd. The new belt acts just as the old belt did, so I don't think it's a belt problem. I cleaned the vari pulley. Is it possible that the pully is bad?