backfiring @ 5200+ RPM..ASAP Please

Trying to get out to test-n-tune tomorrow, but I'm having a major issue.

Car runs great @ WOT or slight acceleration.. Once I hit 5100-5200 RPM+ under full load the engine starts bucking. Sounds like a spark issue backfiring thru the intake manifold.
I pull the plugs, all appear ok. I go out and drive it again, same issue. I get on the interstate and really open it up while watching all my gauges. After about 5-6 backfires I see the fuel pressure drop down to about 20 P.S.I... I get off the throttle and see the pressure jump back to 55 P.S.I....
I'm thinking it might be a fuel pressure problem, but the symptoms seem like a spark issue..
So I try it again. Fuel pressure stays @ 40 P.S.I...Anytime I take engine vacuum away it jumps to 60......Open it back up above 5200 RPM and it starts to run like ****, then the gauge suddenly drops to 20 again...
The pump is large enough to handle the fuel delivery, so that's not the problem...

Here's what I have

Aeromotive fuel system:
External high output Aeromotive fuel pump
83 LB/HR injectors
Aeromotive fuel rail with braided fuel lines
Aermomotive adjustable fuel pressure regulator
351W with edelbrock heads/intake and stage II D-1SC Procharger
Ignition:
MSD Ignition system with box, upgraded distributor, high performance wires, etc.

I'm kind of leaning towards fuel pump, but I'm thinking if the pump was actually going bad wouldn't the pressure gradually drop instead of having full pressure then immediately dropping off at a certain point?? Anyway to actually test the pump? There's no schradder valve on the rail or anything like that. Any help is greatly appreciated.

Hopefully if it dries up outside I can go drive it again.. I'll pull the vacuum hose off and harness off the regulator and go drive it again.. This way the regulator is stuck in one position....
Fuel filter...I suppose maybe. I'll have to get under the car again and see if it has one installed.

well I talked to a couple people today and they gave me some really good ideas.
I explained to them how it seems like a spark issue, but my fuel pressure keeps dropping..I couldn't get it...I found that I was gapping my plugs to much causing them to foul out by the time I warmed the motor up and got it to the interstate.. So I swapped my plugs again and gapped them to .029" rather than .034". I ran it hard and found that the problem went away...for now.

What was happenning is that the engine would backfire from fouling out.. That would cause the engine to draw in excessive vacuum making my regulator drop fuel pressure......I'm sure these plugs will start to foul after a couple hundred miles, so I'm going to lean the engine out just a little bit and see if that helps...Better to rich than lean though..Thanks for the ideas.