Kevin, you also may want to check your Impco regulator fuel pressure on the test port to confirm 1.5- 2 psi during idle and load. It's always tough to isolate a problem that is intermittent. I think the 5/8 vapor hose from regulator to carb is suspect as mentioned and the PCV valve also should be changed. One last thing, I like to use my ignition tester (alligator clip on one end, slips into plug wire on other) onto a spark plug with a decent gap set on it and make sure it doesn't fade during the stutter. Good luck!!