Tractor Repair: Lawn Tractor is wont go up hills, craftsman lawn tractor

Question
I have a 42" Craftsman Lawn Tractor 6 speed.  The tractor works good on level ground except when turning.  Then is becomes jerky.  When I try to go up a hill in 4th gear it just stops.  I have always been able to go up the hill in 4th gear.  The only way to make it up the hill is to shift to 1st gear, and then I can barely make it. What do think the problem could be?  
Thanks
Brad  

Answer
Brad look at the drive belt for the transmission this could be the problem short of that the engine is still working ok just machine slows down if this is the case it could be internal in the ransmission.

Hope this helps with the problem please keep me informed as to what you find.



       Kind Regards Danny Last