The "After-Rev Drop"
 

OK, I'm new to the Mod motor scene, and I don't have very much knowledge about fuel injection at all. Give me a good ol' carburetor and I can make it run like a top. So, I have this question; when I rev my engine, it takes forever for the RPM's to drop back down. I know on a carburetor there is a little dashpot that you could adjust (or remove alltogether--that's what I always did). Is there any adjustment for this on the throttle body on my 5.4L, or is this electronically controlled by the ECM? This new truck is a learning experience for me, and I have already learned alot just from reading this forum. Thanks in advance!

Your 2008 has totally electronic throttle control from software.
There is no external hardware that you can remove since the first Ford fuel injection back in 1985.
Unless there is an obvious malfunction or long time hang there is nothing you can do unless there is a factory software update from the dealer that would be the fix..