got a belt problem

alright guys, this is on the murray. When you put it in any gear and let off the clutch the belt will grab and you move a little bit and then it will throw the belt. I did a little investigating and found the pulley on the transaxle to be slightly bent. I straitened it up as best i could and it didnt seem to make any difference. Then i noticed that the bolts that hold the rearend to the frame were a little loose. I tightened those up and still no difference. The belt stays on in all gears at idle and about half throttle whether you dump the clutch or feather it, it doesnt change anything. What yall think?

Something is probably out of alignment somewhere........How old is the belt?....Is there a tensioner that might be out of alignment?

ive checked the alignment and everything looks good. Belt is quite a few years old.