Missing Under A Load

[redlt499]

Im having trouble with my 5.3, it idles and runs great unless im pulling my car trailier or at a constant speed and try to accelerate. I can make it miss at 35-55mph and around 1200rpm and it will pop back through the intake if you dont accelerate just a bit, maybe 2-5 mph. No trouble codes except for a coil missfire and 2 o2 sensors. Things I've replaced are the fuel pump, EGR vavle,fuel pressure reg, plugs,plug wires, 1 coil, 2 o2 sensors, fuel filter,cleaned fuel rails, replaced all orings on injectors, cleaned maf screen and had it scanned by the GM dealer and was told all he could find was a o2 sensor was showing it was lean(pass side #1) which i replaced. Any help would be appreciated

[Big Whiskey]

It sure sounds like you've tried a lot of the common possible problems. I had a 2000 quite a few years ago, and it started missing and cutting out. The code also showed a lean mixture. I bought some GM fuel injector cleaner from the parts guy at my local dealer. It was pretty pricey, but it seemed to help a little. I ended up fixing it by tapping on the injector coil with a screw driver handle. One of my mechanic friends said that many dealers suggest replacing the coil with a new one, but just tapping on them can fix the problem many times. It's sure worth a try. Good luck.