318 cuts out and dies

Hi guys,
I have a 318 with a P218 engine, after running for about 20-30 minutes, if I go downhill with the mower pto on the engine with start to cut out bad and sometimes die.... it only does it warm, pto on, and pointing downhill (sometimes turning hard and fast)... fuel lines are replaced, pto is new, seat switch is bypassed, pto is direct wired to switch and battery, and I have tried a jumper wire to the coil to bypass the TDM, still does it... also the cylinder head temp (according to my laser temp gun) is at about 310F.. not sure if that is a problem