Delete the edge or update to a Gryphon, Off the torque robbing 40's , replace with a Roush/Borla cat back. If you have to have it loud as hell - Go with some little Magnaflows and Long Tube headers w/High Flows.
The 4six is torque lacking, not enough for a heavy truck IMO.
4.10's - VERY awesome mod, the best for that truck. That and the tune alone will make a big difference..
BTW - Spec charts are here -
http://www.fordf150.net/specs/