Small Engines (Lawn Mowers, etc.): hydro drive stalling up hills, sears craftsman, riding mower

Question
Sears Craftsman 15.5 HP 42" riding mower with Peerless 205-039C hydrostatic transaxle. This spring mower started "stalling" going up hills. Engine running just fine but loses speed, surges and barely makes it up as I feed more power from the motion control lever. Can't hear any belt slipping but will try replacing. General question. What causes these drives to fail and what can be doen to avoid problems? When I purchased the mower the benefit of the hydro over gear drive was that there are no moving parts to wear out.  

Answer
 Hello Stu:

 The Belt is the most likely cause for this problem. I have the same Hydrostatic Transaxle. They give very little problems other than the Belt. Check the Idler Pulleys also.
Hope this Helps.

 Good Luck

 Respectfully

 John