Loss of drive

[p48jones]

I have a 1996 Craftsman Kohler Command 15.5 hp lawn tractor that sill has great engine power and mows fine. However, even though the engine is running fine, there is no pulling power on hills. It will pull on level ground but when I start up a hill it will just barely creep along even though the engine is at full throttle. I've replaced the drive belt thinking that was stretched or worn but this made no difference. it has hydrostatic drive. Is the transmission just gone?
PJ

 

[ILENGINE]

Could be a slipping drive belt. Normally when those hydrostats start acting up they will get a growl to them, which is louder and more distinct than the normal whine like you get if you move the speed selector quickly.