I did it in my 04 same darn truck
pain in the @ss but very doable if u have the patience.
the fronts are a little easier. Basically involes removing the entire door trim unbolting the speaker and putting another in its place.. Rear is a little more involved. If u plan on doing the rear u might as well run wires for a changer and or amp at the same time cause your going to have the tear alot of crap out to do it right. Front seats rear bench. most of the back panals. I don't know why they couldn't have made the speaks accesable

I used alpine 5x7 and sounds awsome. Then switched to an alpine deck and a
subsolution TSSS in the back driven by a 200w M-220 amp and a 6disc mp3 changer, still room for two small persons

in the back damn it sound good in there