Really? 1,000 hours? So glad you let me know that -makes sense. I was starting to shop for prices -they aint cheap. Yes, I am suspecting the blades as well. I keep sharpening them, but I'm not the best at it. The right one always seems to be the worst. I try to regularly clean off the deck -both on top and inside (that's a 2-hr job!) but I do happen to have a fair amount on top right now so I'll check that as well.I'd check your blades first as it would be rare to have to change that belt unless you have over 1,000 hours of mowing! The only other thing it might be would beto enough grass build up on the top of the deck to hold the belt tensioner from operating properly.