1999 Isuzu Rodeo Question Electrical or Computer Porblem?

This is actually an Amigo, but most everything is the same as a Rodeo.

I had the engine rebuilt on this toy about 3,000 miles ago. Since then, the check engine light periodically comes on indicating that there is a misfire in either cylinder 3 or 4 (it varies from time to time). The car runs noticeably hard on 5 cylinders when this occurs. The problem is that it can go weeks without happening and then start for a bit, and then stop again. This seems to happen most often on a cold engine when the weather is damp. None of the local shops have been able to diagnose this problem. It does not seem to be mechanical as it is intermittent and when running on all 6 cylinders, runs well. My initial thought was perhaps faulty wring to the coils. Does anyone have any ideas?