sounds like electrical....like defective safety switches or bad pto clutch....if a switch case is broken....it can swell with heat pulling the contacts apart.....then cools and comes back together ....something is shutting your PTO clutch off....check your safety switches for anything obviously wrong....heres a set of diagrams that might help.....can you take pictures for us?..............do you know how to use the continuity setting on a multimeter?