98 4.6 73,000 miles:
i took my IAC/throttle body/EGR valve completely off this last weekend and cleaned both completely out. Lots of carbon build up. After I got them all back on and a new battery in my truck, my truck idled high too for about 50 miles or so, then it settled back down, but still runs a little faster and "peppier" then before i did the cleaning
Im thinking that if you unhook your negative terminal, turn on the headlights for a while, then turn them off and re-connect your battery, your truck will settle back down. You might also consider doing this throttle body cleaning to your truck,it's amazing how much better your truck will run after all the carbon is cleaned out.
If interested, check out my thread on "rough idle" on page 2 in the Engines forum.