I just replace the engine head with a new one because old one was cracked. Before I replaced it truck would only start on ether. Same issue with new head. Truck will only start on ether or when engine is cold if you hold throttle body wide open. Timing is correct. Once truck starts and timing is adjusted to 5 degrees BTDC truck runs great at idle but just touching the throttle makes engine fall on its face. Timing has to be advance considerably to open throttle body to rev engine. With timing advanced engine of course idles way too fast and runs a little rough and still hesitates a little when you open throttle. Good fuel pressure and injectors all working with them pulled from manifold. Avpro rebuilt computer a couple years ago. It acts like distributor timing advance not working but I don't understand why it won't start without ether. What am I missing here?