I have a Craftsman VTS4000 riding mower and it slows to a crawl after cutting for 15-20 minutes. The engine is running normal but the mower slows down. After cleaning grass from underneath, it runs normal for afew minutes and then slows down again. I keep it clean, so grass cannot be the problem.

Hi,
It sounds like a problem with the drive system, most likely the hydro. Is it in warranty?
Peace,
Clarke