Eric, you might check the action of the throttle bore air valve with the engine off; be sure it's moving smoothly throughout it's range, and that it retains resistance to downward movement for awhile after the engine is stopped - that's a quick check for retained fuel pressure. Also, a check of the O2 duty cycle via the round diagnostic pins 2&3 might give a hint towards the problem. (if you haven't done this, do a search herein for exact procedure using a Sears meter). Check it with the engine cool, and well warmed up, at idle and at 2500. Then post results and see if it's abnormal, and what to do.
DG