engine only runs rough when a/c or heater blower is on

the strange thing is this only happens down the road and at a constant speed if I push hard on the throttle it smooths out and its any setting of a/c or heater I have used inj. cleaner octane booster keep air cleaner blown out weekly all other time this motor runs great most my peers believe this truck has a v-8 headlights or load has no effect to this problem

I have the same issue with my 2002 Mazda B4000 (4.0, 6cyl.). It had a rough idle when at a stop, the whole truck would shake. I had a tune-up (plugs and wires) and it seemed to run much better. Later I discovered the rough idle returned, but only when I turned on the heater, defroster, air conditioner, or anything involving the climate control (feels like an engine miss, about every 5 seconds) When I turn off the climate control the normal idle returns.

Hey At this point I have no great ideas. I think getting this thing on a scanner and seeing what is going on is the best bet. Its a strange set of symptoms. Matt