so are you saying it was a lifter problem?

I have the 3.9L V6 and its a magume and its got alot of power because when i had my truck back into they other guys insurence company paid to get it fixed and for a rental truck it was my truck all over again but 4X4 and with a V8 unsure what size V8 but my V6 has the same amout if not more then that V8 although the rental truck was a 2008 not a 2000. the 2008 truck had the problem you guys are having. i just drive the **** outta of it lol.

Ever clean or replace the IAC?

Lifter- No.. Fail me.. I'm an idiot.. the Rocker arms.
IAC- Yes and did not change anything.

Dealing with the same rough idle on my '99 with the 5.2, I dug in and double checked everything. Found a very minor vacuum leak at a joint in the plastic vacuum line that runs across the firewall up near the windshield washers. Cleaned the IAC AGAIN (replaced it as it fell apart when I pulled it). Cleaned the MAP sensor with CRC QD electronic cleaner and let it dry while I installed a new PCV valve (had cleaned it a couple times). Backed it out of the driveway, stomped on the GO pedal and did a 100' one-pedal burnout!!! REALLY!!! Darned thing is, the next day it was back to normal power (the MAP sensor must have been wet). The air filter hose was off still, and it sounded GREAT!!!

I still have the loping, but it is nowhere near like it was. It is more even, not as rough, and I can live with it. It has ruined my muffler by shaking a baffle loose inside... that's on my fix list.

Just some food for thought.

The thing is with a loose rocker arm/bad rocker arm, when the cam pushes up on the push rod to push the rocker arm up, being it is loose/bad it will not push the valve all the way open, thus causing a lean/rich condition either it does not get enough air in causing a rich condition or does not get enough of either..

(Thats how it was explained to me)

Which will run like its out of time, or like a vacuum leak and so on.. this and the plenum needs to be checked.