What is causing the spark knock at higher rpms on my f-150 v8 4.6 triton?

I would suggest checking the timing and timing advance with an advance type timing light. This type of timing light has a dial on it. First check the base timing. Then slowly increase the rpm to the rpm that the engine usually spark knocks at and see what the timing advance is at this point. Check your reading against the factory spec. I'm sorry but I don't have that spec handy. When the engine begins to spark knock the computer should adjust the timing to make it stop knocking. if it isn't you may have a bad knock sensor.

There might be too much fuel going into the cylinders caused maybe by bad injectors or coolant temperature sensor or O2 sensor. Do you have any check engine lights?