Why my Toro ss5000 zero turn tractor shut off after engaging handles?

When I start my tractor the engine starts fine and it keep running until I move the handles from the park position to the forward /reverse position. As soon as I move these handles the engine shuts down. I over road the seat safety seat but I still had the same problem. Occasionally, the the tractor would move forward or reverse for about 15 seconds the shut down. If I quickly move the handle by to the park position the engine continues to run. Sorry for being long winded but I can’t figure this out. Please Help.