please help-unsolved problem

[Moto Mel]

You need to get this fixed real soon because backfires through the intake could damage the throttle plates and possibly some of your sensors.
Double check your plug wires for proper placement, then change the coil for a known good one. Then check your cam timing. Usually an engine falling flat like you describe the problem is a huge vacuum leak or no fuel, backfires; plug wires wrong, bent valves or other electrical issues.
Before you start you might want to reset your ECM by disconnecting your battery for a couple of minutes and then start your diagnosis of the problem.

 

[F150hybred]

High engine loads will effect ignition demands (high engine loads = more spark energy needed to ignite the air fuel mixture). I would be checking the resistance in the ignition wires and from there, try a known to be good coil pack. barring those being ok, I would be looking at possibly bad spark plugs.