The AC voltage seems fine, so that'* likely not the issue.
It might be good to meet up with someone who has scan equipment, because the way you describe it could open up numerous possibilities, from crank position sensor, to ignition power dropping out, to even a bad ground, and everything in between. The scanner would take a lot of the guesswork out of it, so that you are not throwing a bunch of parts at it that it may not need.
Also, is there any trouble codes present? That may give you some place to start as well.