Zach, Mike actually has the muffler from my dads F-150, it was a SI/DO Borla Pro-XS - it was longer than the XS i had on the Ranger and gave the 5.4L a very docile sound.
Honestly a straight through muffler is going to give you a "poopy" sound with a 4-banger, i would stick with a chambered muffler if you want that "growl".
If you decide to go with a chambered muffler i would go to a 3-chamber. Edelbrock makes one, Flowmaster 50 series, and the Magnaflow 3-Chamber - would all work.
If you go to a "straight-through" design muffler, be sure to stay in the neighborhood of 16-20" in length. These types of mufflers seem to get louder as they get smaller.
Hope that helps.
2oo1 Ford Ranger SOLD!
Proud Owner of a 2005 Silver FX4 F150