Transmission ???

I am fixing a Craftsman YS4500 model number 917. 276600. The engine is a 22HP B&S intek model 407777 type 0607 E2 code 050812YG. I noticed last year that the mower seemed to be going slower than normal. After some engine work after a fire it is running like a top again. The problem now seem to be the Hydrostatic transmission. The mower is not reaching top speed and will barley climb any incline. It almost stops going on a slight incline. Is there anything I can do to the transmission to fix this issue? Any help would be greatly appreciated.

Could be a worn/slipping belt, worn pulley, improper belt tension OR the trans...... look on your trans for a make & model sticker, post that info. replacement belt P/Ns and tension adjustments should be in your machines owners guide.