ARGHH!!! I'm running out of things to clean/check/replace, here. For any resident 5.0L exorcists, here's my current demonic possession: Cold or warm, the car has an issue with surging/bucking at cruise and losing about 25% of its power at WOT. There is the occasional small mini-backfire out the exhaust during these little fits of the herky-jerkies, which I figure is caused by a rich-running condition. Except during periods of Satanic influence, the car idles fine; otherwise, while possessed, the car idles almost like I'm running a lopey cam. This presence of evil isn't constant, and it seems to come and go without any rhyme or reason, totally independant of ambient or engine temps, driving habits or distance, humidity, etc. This sort of thing has happened off and on since I obtained the vehicle about four months ago, but it was initially due to a severely clogged PCV screen/valve, disconnected/rotting/split vacuum lines, and/or a dire need for a tune-up. Since then, partly due to these random symptoms and partly because I'm totally OCD about making things run perfectly, I have dumped the following blood, sweat, and tears into this apparent target of El Diablo: -Replaced EGR valve and cleaned passages -Replaced IAC and cleaned passages -Replaced all 8 injectors with new 19# four-hole units from 4.6L T-bird (due to 3 cracked/leaky stock units) -Replaced cap/rotor (brass), wires (Bosch), plugs (Motorcraft) -Replaced all filters/fluids - air, oil, fuel, rear diff., tranny, etc. -Given two Seafoam treatments through PCV valve and gas tank, and hosed the snot out of the throttle body/upper intake with Seafoam Deep Creep -Adjusted TPS voltage -Replaced every little piece of rubber vacuum line, checked all hard plastic lines for leaks with carb cleaner and watchful eyes -Replaced PCV valve grommet and screen -Cleaned up every ground connection in sight -MAF wires cleaned and reset ECM -No trouble codes found, no CEL coming on All of this has been going on since the day I drove the beast home ... with the evil influence of The Beast hiding under the hood with it, apparently. Any suggestions/ideas/chants of divinity shall be met with bowing at thy feet and much gratitude (up to and including the kissing of feet).