Hey, I've got a 99 5.7L, auto trans, air, 4x4 - 81k. I did a tune on it in December with all delco parts. New dist, rotor, wires, plugs. Replaced egr last year, along with tps and iac. The engine lopes once in a while, like around 700rpms down to like 400 rpms in gear. Sometimes it will drop down to as low as 200 rpms. Sometimes it will die is you shift from reverse to drive. I thought it was the iac valve, but now I'm stumped. No engine light. Fuel pressure is at about 59 while idling.
Also noted that it misfires between about 850rpms to about 2200 or so while accelerating. I have replaced the MAF with a known good working unit, so I'm ruling that out as well. Have sprayed carb cleaner around the intake as well as the tubing that goes to it. No change in RPM. No codes.
Any ideas would be greatly appreciated.