jffr,
The shop that originally installed the EFI system works almost exclusively on high end cars and exotics. I met him years ago when he was preparing my former partner's Audi for racing, and he worked on my XKR, installing a pulley and tune. Typically, on a day in his shop you'll see two or three Nissan GTRs, same with Audi R8s, a Ferrari or two, and some oddballs like a Spyker, Merc AMG GT, etc.
When I first had the issue, I brought it back to his shop several times, and he tried several fixes but the problem persisted. Then he got so busy, he just never had the time to work on it and frankly I got frustrated with his inability to find the time or the problem, and I took it back to my normal mechanic who works on all of my cars. He has had the car for the last couple of months and thought he had solved the problem, called me to pick up the car, and in his parking lot while we were talking, it started to stumble again. Over the past three weeks since that day, our attempts to contact Holley technical support were unsuccessful, and the problem persisted. I finally gave up, I want to be able to drive my car before I get too old to do so, I'm 67 and having surgery next week on my right leg, so I won't be driving it for a while anyway, but I hope to do so soon, and I'm not willing to feel like I'm not going to make it home on any drive I venture out on. I wish that the fuel injection worked in my case because it made starting the car a pleasure something that hadn't happened in the previous 18 years of ownership.