fuel pressure issues

[mustang98gt]

I greatly appriciate any assistance in this matter: I own a 1998 Mustang GT 4.6 liter (manual). I have just installed a Walbro GSS3017 255lph fuel pump after my stock fuel pump started to fail (loss of 6psi and going). Since installing the pump and sealing it all back up, I immediately noticed problems with engine performance while driving. It would start to 'buck' wildly at just above idle speed and through a small portion of accelerating up to WOT. Pressure at the schrader valve was 90 to 100psi!

I looked at my 1998 Mustang GT to replace the apparent (to me) faulty fuel pressure regulator attached to the fuel rail / fuel injection supply manifold, while looking at a Chilton's and Haynes car manual. Wouldn't you know it, the 1998's are different than the 1996/97 4.6 liters. The 96 and 97 you can replace the regulator by detaching it with an allen tool. The 98 is WELDED to the fuel rail!

I have replaced successfully the 98 fuel rail with a 97 ford crown vic police car fuel rail and added a BBK1707. I adjusted the regulator far down as it would go like the instructions said. The best I can get it down to is 65 PSI. The voltage at the pump is 12.5 volts. Both the Haynes and Chilton's manuals say the voltage is suppost to be 10.5 volts. Right now my car runs okay but it still bucks somewhat at just above idle speed. I had a full tank of gas and I get approx 300 to 320 miles out of a normal tank. I am down to 1/4 of a tank of gas and I only have 150 miles to show for it. The gas gauge is dropping faster than this last Iraqi war we just had!!!

Is my pump pushing too much fuel pressure and causing my car to still buck at just above idle and make the check engine light come on (no brainer on the MIL light). I saw a product from Weldon called the 14000 Dial-A-Flow which can change the voltage with a dial. Could this be a solution to lower power to my Walbro fuel pump power? Should I consider replacing my fuel return line with a larger one (say by as much as 2mm) to reduce pressure?

My major concern is fuel consumption but drivability is a big issue as well.

Here are the aftermarket bolt on power adders I have implaced on my car just in case you see a possibility of a conflict of any sort.

March underdrive pulley system
K&N air filter
Cervini's Ram Air hood w/ ram air kit
9mm spark plug wires w/ autolight double platinum spark plugs
70mm throttle body
Bassani X pipe w/o cats 2.5 inch (malfunction indicator light eliminators attached)
Flowmaster 2 chamber 2.5 inch
Jet Performance Superchip
BBK 1707 Fuel Pressure Regulator
Timing adjustor set at 16 degrees

Car is at 107,000 miles (3/4th of it is highway)

Thank you for any help and recommendations you may have in this matter!