Misfire - Ignition Advice

Pana.Mopar said
It's been there for ages. Its usually once the car is hot and above 1,500rpm on the throttle. Doesn't do it at low speed or cruise.

So you are saying that heavier throttle causes it? I would suspect low spark voltage. Bad coil wire, bad coil, something wrong in the ignition module, or LOW 12V SUPPLY VOLTAGE to the unit, caused by a number of things, including mis-wired (are you using a ballast and is it supposed to?) or other harness problems

Try separating the ignition system from the harness and 'hot wire' it direct and see if that makes a difference