Small Engines (Lawn Mowers, etc.): Sabre looses forward power, old john deere, forward power

Question
I have an 8 year old John Deere Sabre.  When I use it for more then thirty minutes, it looses the ability to go up any incline at all.  It has an automatic transmission.  If it is the transmission, is it easy to replace and is it worth it?

Answer
 Hello Walter:

 Check the Transaxle Cooling Fan. Are the Blades OK? Is there a build up of Grass and Dirt on the Transaxle? This is the Hydrostat Drive Transaxle. The Cooler it is the Better it works. Check the Belt for Stretch when Hot. Belts Stretch and Shrink. Hope this Helps.

 Good Luck

 Respectfully

 John