Small Engine Troubleshooting Problems? Ask a Mechanic Now.
Hello. My name is***** will be happy to assist you.
Your transmission, is a manual shift model. Do you have the same problem on level surfaces? Is your new belt an OEM belt, or an aftermarket belt?
First, double check, to make sure you have the correct belt. The part numbers should 130801. Next, check to see if your belt is tight, because if your belt is slipping, this can affect the performance of your transmission, when going up a hill.
Also, check the inner running surfaces on your transmission pulley, and the pulley that bolts to the bottom of your engine. If these pulleys are worn, your belt will have a looser fit, and will slip when under load. Your mower is almost 16 years old, so I would definitely look closely at pulleys, for the possibility of excessive wear.
We can continue from here. Thanks!