Check and see if the spark plugs have been changed on any 04 - 07 5.4L engine. 4.6L do not have the problem, only 3v 5.4Ls. If not, have the dealer do it if you agree to buy it and replace with the 2008+ better Motorcraft plugs.
All of the features you stated on page 1 mean you will want a Lariat pkg, 07 - 08 FX4 Luxury pkg, or a King Ranch. 5.4L, with the 3.73LSD ( axle code B6 ) you will love it. Best powertrain. Handles 33s and 35s just well. 2005s were known for a faulty injector issue, but anything over 30k miles would most likely have the issue fixed as it happened early in 2005 5.4Ls lives. The brakes seem to be a weak point in these trucks, 2004 - 2006 have been known for seizing calipers up front ( my drivers size left one is actually, and has been for months, cant afford to fix it, until a couple weeks when my job pays me more ) anyways thats probably going to be your only powertrain fix, if ball joints are in fine working condition. Throw on some new pads and rotors while your at it and you'll be set for them 35s.
Want anymore infomation, join the darkside website, F150online, and post what you want in the 2004 - 2008 section, and you'll get a swarm of replies. Theres one going right now actually you may be able to find helpful for yourself.
http://www.f150online.com/forums/2004-2008-f-150/414663-looking-buy-f-150-need-info.html
And, 2006+ offered the Supercrew and 6'5 bed configuration, definite WIN
buy a ford..trust me..its a smart move
x2.