Sorry folks,
but popping/backfiring on the overrun is a different matter altogether from a misfire under load.

It's the result of a (small) leak in the exhaust system, the closer that leak is to the engine, the more frequent and more pronounced it will be.
Trace the leaks using a length of windscreen washer tube as a stethoscope, seal them up and I bet the problem will disappear.

Ken