2005 Buick Rendezvous engine cutting out

We have an '05 Buick Rendezvous. My wife is the regular driver. She had started telling me that she smelled gas when her car was near full, then the gas hand stopped working regularly. After you fill the tank, it works okay until you are around a 1/2 tank then it goes haywire. 2 weeks ago, she went to leave the house in the morning, and she could not get it started. It just kept turning over. I went out and told her she might flood it. I waited a few minutes and while keeping the pedal pressed to the floor was able to get the car started, put it in gear, eased off the gas to back out and it cut out. Cranked it the same way again, and rode the brake pedal and gas together, eased it out and drove down the street and around the block. As long as I kept my foot on the gas it wouldn't cut off. We had it towed to our mechanic shop. It worked perfectly for him from the time it came off the truck, never cut off. He went ahead and replaced the fuel filter. It worked fine for the next 1.5 weeks & then the same thing occured again, 3 mornings ago. Before I pour more money down in it or on a fuel pump, I wanted to get some other ideas, i.E. - Oxygen sensor or some kind of relay that might have affected it like this.
Thanks,
EW

Car will pretty consistently do the following when started first thing in the morning. The engine starts, acts like it is trying to run, grumbles a bit (or a lot) and then dies out after a second or two. Usually starting it again will cause it to start and run. This only happens after letting the car sit overnight. Starts during the day after the initial start are usually fine. Once running, the car runs great - no hesitation, stalling or other issues. No codes displayed when scanned, no warning lights displayed. Here is what has been replaced by me or a shop recently (either for this issue or another problem):

- Fuel pump / filter (shop)
- Crankshaft position sensor (shop)
- PCM (me)
- Ignition switch (me)

After I replaced the PCM (to correct a crank / no start condition), I did not do the crankshaft relearn procedure which is recommended, as I don't have the Tech II scanner needed. Is this important? What would be common things to look for next? I read the fuel pressure regulator can have a slow leak which causes gas to accumulate which results in a too-rich condition when first started. Any help to guide me in what to try next would be most appreciated.

Car just stalls out and than restarts, I replaced mass air flow sensor recently.

Thanks I going to change out iac valve because the idle seams very low at times low as 600 rpm to 800 hope this helps.