Had a misfire on cylinder 3. Changed spark plugs, ac delco iridiums spaced at .042 - .043, changed air filter, tightened up pcv hose, cleaned throttle body, and changed front drive shaft CV joint on transmission side (unrelated but it was broke). Scanned for misfires, looked good, but misfire on cylinder 3 came back hours later. Swapped cylinder 2 and 3 ignition coils, problem completely went away. Scanned ignition timing and fuel trims, scanned for knock and misfires. Long story short, it's running like its brand spanking new. Must have be corroded or otherwise bad connection at the igition coils. Will clean them in the near future. I enjoy working on this hummer. The best part is, it's so easy working on it. Did all of that in about 2 hours and i was taking my time working pretty slow.