[quote][/quote]Forgot to mention that is has aftermarket electronic ignition under the cap (no points).

Is this a conversion of the old distributor? If so make sure the ground wire from the breaker plate to the housing is intact and good. I had troubles with an Oldsmobile and the breaker plate would intermittently loose ground at various vacuum conditions causing a stumble. As the vacuum advance was working the plate it would loose ground. If it was removed add one and see if it helps.