per owners manual, chk tranny oil level and fluid condition - also make sure tranny cases are free of trash and grass clippings to avoid overheating - carefully chk condition/function of tranny drive belts. also chk for any damage to tranny cooling fans. Always operate engine at full RPM to gain maximum cooling.
Lastly - if possible - change tranny fluid and filter (if so equipped) - old or overheated oil can lose it's ability to work correctly..
NOTE: Do NOT use garden hose or power washer to clean. Use compressed air or leaf blower.