I just had a bizarre one a few weeks ago.
It was on a 3.0L GM in an H60.
Turned out to be the alternator!?

The only way I can figure it, is that it was leaking enough AC to cause the ign. to pick it up and missfire.
I only found it by accident. Was trying to track down some noise from the front (because of miss-fire I was working my way back to the timing chain).
Pulled the belt and oila, problem solved.

I honestly don't think this is your problem as NO ONE I know has ever seen this but I thought I'd pass it on anyway...