BTW, I have basically the same mower as above...42" Craftsman model 917.270610. Have a couple pictures if that will help...not sure how to post them though. Let me know if it will help and ill figure it out.
I have the same one. I'm assuming my problem is similar. When I engage the pto the blades spin fine. Normal speed. But when they encounter any resistance (grass longer than 2 inches) they slow or stop. Loose/worn belt? Can I just adjust a tensioner pulley like a truck? My field is getting out of control!