Ok, 8 mos ago I made the HUGE mistake of letting someone else work on my car (long story, but involved dyno time). Anyway, my car ran pretty good when I dropped it off - would get to 12psi @ redline, but seemed like it could make more hp (re:tuning). So I drop it off, they tune it up (plus, wires etc), then tell I'm not getting enough fuel to motor so they can't dyno tune it. I pick it up and it runs like sh&t. I refused to take it back (another long story) and fixed my fuel problem myself. I changed the fuel pump, filter and injectors and cleaned all fuel lines. The problem is the car runs really stought for the first 30 miles, then I start having a problem above 4k (hesitating or leaning out). I rechecked the fuel system, then came on here and did a search on lean or problems at high rpm's. Seems a hesitation points to spark plugs as a possible culprit, so I just went out and pulled one. It is an AC Delco R43TS gapped at .035. How do these stack up against the NGK's or 104's? I'm sorry to say I do not know what plugs were in there before I dropped it off. BTW fuel pressure is @ 43psi idle and climbs to 80-85lbs and I don't think its a fuel problem unless the fpr or fmu are leaking. Thanks in advance for any help!