Ok, well, after reading some others posts about this sort of thing, I figured I would try the FPR. (Fuel pressure regulator).
Got the old one out, new one in.
Cranked the key on/off, on/off. No pressure building in the line. Crap.
Started right up. Ran for awhile. No leaks. Turned it off. Soon as the key was in the off position the pressure was at 0 again. Crap!!!

So this means what, I have to replace the whole fuel pump/sending unit/etc junk at almost $300 now?

Ugh.
Any other options?
If I spend near $300 to get a sender/pump unit, and it doesn't work, I'm burning this stupid POS to the ground.

You may have a injector stuck open. Pull the injectors and inspect them. Also pull the plugs and see if one of them is much darker then the others.

Dan, go back to the bottom of page one. I just changed them.

I went and put in brand new factory L36 injectors.
The old ones were sticking, and dirty. These just went in last night.
I've eliminated the injectors, and now the FPR.
What else can it be?
Gotta be the check valve in the pump sticking open, right? Its never, ever been able to prime at all. I can't even budge the gauge no matter if I key on the pump 2 times or 20. It just wont prime, and no matter what I do, as soon as the car is shut off, it drops like a rock.

But what gets to me, is that it will start cold without the slightest hesitation. Cold starts in the morning barely need to touch the key to get it running. But there isn't pressure in the rail then either, so I don't understand why this only happens when its hot. And only after a couple minutes of sitting hot. If I turn it off, wait a minute or two, and start it, it turns over without any problem. It refuses to start if its been sitting for 5-10 minutes or more. I just don't get it. And its completely 100% repeatable. Every time. Nothing random about it. It does the exact same thing in the exact same circumstances.
Cold start (off during work shift or overnight) turns over fine.
Hot start (if sitting more than a couple minutes) takes forever to crank over
Hot start (if sitting less than a couple minutes) turns over ok.
Will not prime the rail... ever. Not cold, not hot.
Always drops pressure instantly upon key off, hot or cold.

Here is what I'm thinking of trying to test. I want to test if the pump will pump faster when its cold than when its warm. I think I'm going to jumper the relay terminals when its warm, see if it will eventually prime the rail, and try and start without the aid of pressing on the gas. I'm not sure that the "clear flood" command is actually whats starting it. I think its just cranking time, independent of if the pedal is touched or not. Which means its not a case of fuel leakdown into the cylinders, but something else.
I mean, it has 118k on it. Its a 2004. What are the chances the pump itself is getting heat soaked, and taking longer to crank over when hot? Not to mention the check ball is completely stuck open, hence why it never builds pressure in the rail, because it isn't constantly running...it just spits out a bit of fuel which just runs back into the tank through the open check valve.
Am I way off base here, or does this sound plausible? There are only 3 ways out for fuel to go (assuming no external leaks, which it isn't doing either).. leaking FPR to return line, leaking injectors, or open check valve in the fill line, right?

I would look in to the check ball, With new injectors it'* unlikely a bad injector. The FPR don't sound like the problem either, that runs of engine vacuum and you don't have much at startup or at first key turn.

Likely the issue is the checkball in the pump. It'* internal and non-servicable.

However, the pump can be replaced by itself. Takes a little more work than simply putting a whole new canister into the tank, but it'll be much less expensive. I've had great success with TRE Performance fuel pumps. Put one in my car and truck about 4 years back w/o a single issue. Prices are right as well. High flow for the car was $80 at the time.

Just thought I'd post a follow up in the thread for those who might search it.
I believe it is the check ball valve in the pump. However, the problem went away on its own.

I have changed jobs, and am driving a lot more now, 2x the distance actually. 1.5 hours worth a day, times 6 days a week. And using a different gas station as home base for my fill ups. Not sure if that made a difference or not. But it just happened a couple weeks ago. I suddenly realized it wasn't having trouble starting anymore. And sure enough, I went to check the gauge (which is still hooked in), and it holds line pressure perfectly.
So, could be a combination of things, longer driving, different gas, going up and down a lot of steep hills creating pressure differentials... the locking gas cap I put on... who knows. Probably just pure luck or time.

But its all good. For now.