Try checking the resistance of the spark plug wires. They should have a maximum of 1,000 ohms per inch. It sounds like you have spark plugs and/or wires breaking down and missing under load.
Jerry


"It is better to be silent and be thought a fool than to speak and eliminate all doubt!" - Abraham Lincoln
Cringe and wail in fear, Eloi- - - - -we Morlocks are on the hunt!
There is nothing noble in being superior to your fellow man; true nobility is being superior to your former self. - Ernest Hemingway
Love your enemies and drive 'em nuts!