The '04 to '08 F-150 doesn't have an IAC, unless it's an '04 Heritage Edition. It uses the ETC (Electronic Throttle) to control idle speed. So that's out. However, the throttle body could be all gummy but he's checked that.
BTW, TNF150 - In one post you indicated it was an '04 and in another you said '06. Which is it?? The are specific driveability issues for different years and need to know which year we are dealing with to see if there are any specific TSBs relating to your symptoms.
Take care.
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