Unkown Ranger problem

Timing is dead on, total advance is just under 28 degrees. Yes it has a mass air unit and, as per my more reputable mechanic, it is working correctly. TPS is in range and working correctly. There are no active or hardcodes in the ECM. This hesitation problem occurs hot or cold. It tends to be more preveliant when it's hot and the probem is getting more frequent. When it starts to act up, if I blip the throttle a few times, it will correct itself. We've checked the fuel pump relay and all it's associated wiring. They're ok. We changed out the ignition module, at a suggestion by the local Ford dealer. That didn't correct the problem. The one thing I notice, the fuel pump wines, rather loudly once the truck is up to operating temp. When the hesitation starts, I notice the wine goes away with the motors starting to hesitate. We put a fuel pump pressure gauge on the pump and it shows 22 psi. Just for shits and giggles we r&r'd the pump and filter and it did nothing to improve the system psi. The problem with this problem is, it's not consistant. Although each of the 3 mechanics who've looked at the truck have experienced the problem first hand, when they've gone to do checks on the motor, it runs perfectly fine. It's a Ford Each of these three mechanics have told me they consider this to be a fuel system problem. They're concern is that the fuel PSI is within the tolerence, it's just on the low side. There has also been a question that the fuel system may be vapor locking, due to the low fuel pressure. But, correct me if I'm wrong, EFI fuel systems aren't supposed to vapor lock, are they?

Hey that's ok.
It hesitates when it's hot or cold. The pump doesn't wine when it's cold.
The pump whines when the truck gets hot and the wine subsides when it starts hesitating.
The pump was replaced. The old pump was showing 22 PSI which I'm to understand was on the low side. Unfourtunately the new pump is only showing 22 PSI as well. Just FYI, the fuel filter was replaced as well and this has the EFI pump mounted on the frame not an in-the-take pump. I understand this model truck had an "option" of having either pump.
Let me know what ideas you are chewing on.

Ok, will do. I'll have to take it to my mechanic since I don't have a high pressure EFI fuel gauge of my own. This may be a few days since my mechanic isn't opened on the weekends.

The de-icer made no real change (it had an almost full tank of gas). One thing though, I did a hot re-start on it yesterday while grocery shopping, and the thing wouldn't stay running. It would run for about 15 seconds, it started shuttering and then died, irregardless of how hard I pushed on the throttle. I also noticed, when pushing on the throttle to try and keep it running, it sounded like it was back firing up through the intake. I let it cool down for about 30 minutes and it eventually ran. But, it still did it's usuall hesitating. This problem is getting to a point were I can't run the truck 5 miles before it starts acting up. I have an appointment for Wensday with my mechanic to re-check the fuel psi. I'm going to let him know of your idea to test and run until it acts up.

Will do! Should know something Wensday.