That seems to match up my symptoms pretty well.
Not getting the multi-strike in the lower rpms like I should be, but once it kicks over to single strike mode, (and the different fuel and timing map) at the 2k mark, it runs fine.
This is what most people are referring to as a "low grade misfire" on various forums, just no one ever really got to the whole multi strike at idle thing.
GOOD JOB!
Please post up what you find.
The truth is that the F150 series is about the most bulletproof truck there is, my last one had almost a quarter million miles on it and I actually teared up when I traded it in (on another F150 of course).