Have you dynoed the car on a wide band, bud? Sure, it's possible to run rich at idle, but Dollars to donuts you're running lean at WOT. Hard to believe you still have the stock fuel pump. That combo should be good for 290 or so rwhp, but I doubt you're actually making that with the stock pump. That stock pump is really only good for 300 hp at the crank or so.
It may sound biased because I've got two sale, but it's the truth and I'm sure others will reply the same way I did.
I've got an old walbro 255 and a new GSS340 (also 255, but a high fuel pressure pump). The 340 is new and comes with the fuel pump bracket and everything for 100 bux, and the old one is used, but ran perfect and I only want 50 bux for it.
Chris