Engine Stumble Above Idle

[dreman]

I recently got in my truck, fired it up, and tried to drive through the parking lot. It stumbled and had no power, so I thought it might be the fuel filter. No SES light. I replaced it, and no change. Then it just died, and wouldn't start again, so I had it towed home. I found the fuel pressure to be 40-45 psi, which I understand is low, so I replaced the pump. The gas gauge hasn't worked in a while anyway. I went ahead and changed the plugs, wires, cap and rotor while I was at it. Now it fires right up, but still stumbles anywhere above idle. It has power now, but the SES light comes on. The code reads as a P0302, or a misfire in the #2 cylinder. I checked the wire and plug, and then I put the old ones back in that cylinder with no change. At steady cruise the SES light blinks.

 

Any ideas? Oh, yeah. It's a 1999 GMC Sierra Std cab stepside with a 4.3 V6 and auto. 252,000 miles.