Originally Posted by zer0signal667

Sounds like it's misfiring on one cylinder. My escort was doing the same thing a while back - fine at idle, misfire under heavy/moderate load. I changed the plugs and it was fine. Maybe the guy who did your plugs didn't gap them properly, or didn't use dielectric grease on the terminals and they corroded, or one loosened and is leaking down compression, or maybe a wire is shorting or is torn.