I take it still drives but won't pull a hill? Have you tried changing the trans fluid?

You have the Tuff Torq K58 trans, it's a K46 with a charge pump addition. Life of a K46 is about 900 hours, slightly better for a K58 I would assume. Heat is the main destroyer of transaxles. Keeping the transaxle fins clean is a must to have it last. See the link attached for how to rebuild a K46, but it is very long (72 pages). Change the fluid may help and is cheap - use 5W50 synthetic motor oil - 2 Qts. Some have had great results just sanding out scratches on the internal parts.

Here is a link that might be useful: K46 rebuild

I looked at the rebuild post I show above, especially see page 45 post 445 about resurfacing the parts inside. That page also talks about how to change the oil. Read every page and you will be an expert on transaxles. By the way check the simple thing - is the belt slipping?

have changed fluid and belt already....good when flat nothing on slopes.....

Make sure all the drive belt idler pulleys are free and spinning and that the tensioning mechanism is functioning correctly.

Since you changed the belt, did you use a real JD OEM belt or a pretender? Are you absolutely sure the belt is routed correctly?