What kind of O2 sensor did you use? Anything but ac delco or NGK will be bad...

Hi all, I know I haven't posted for a long while but when reading this thread I just had to jump in.

Sounds like the fuel pump to me. It may be working right until it gets a little warm, and then fuel pressure would drop. Try hooking up an external fuel pressure gauge and see what happens.

The symptoms are exactly what I'd expect with low fuel pressure.

Grease Monkey here again. We figured out that it was nothing more than the O2 sensor. I'll make a long story short to save you all some reading.
We first thought it was the TPS (Throttle Position Sensor) so we tried replacing it.
Then since the TPS didn't fix the problem, we put the old one back in and returned the new one.
Next we replaced the O2 sensor, this made the problem better, but didn't totally resolve it.
Next we checked the ECM codes, we found that the O2 sensor and the TPS were both malfunctioning. Which was strange since we just replaced the O2 sensor.
So we reset the computer (disconnected the battery) and tried it again, this time only the TPS was broken.
So we took the car to a shop and had it calibrated (Yes, they must be calibrated, the Chiltons/Haynes guides neglect to mention that).
Ca-Ching! Problem solved. It turned out to be nothing more than the O2 sensor, but since we had screwed up the TPS'* calibration, we caused the save symptoms elsewhere. ARGH!