If the plugs are the same style as the factory 3 valve head spark plugs there is no adjustable gap on the plugs.
You said that it was running well. Was it running well until you replaced the plugs or was this just a try to get rid of the problem. When the issue started were you just driving normally or was it a racing type senario? Sorry for asking so many questions but without being able to actually look at the car I need to ask as for as much info as possible. Did the kit include something that changes the pcm programing? Have you contacted Edlebrock to see if they have any ideas?
If the problem did not start until you changed the plugs i would recomend getting a set of the autolite plugs and put back in the same ones that came with the kit.