Removing tank is pretty straightforward, as was described.
Remove the bumper and the trim piece that fills the gap between the bumper and tailgate. (I don't have one, but I'm assuming if you do, it's easier with it off) Bumper is very easy to remove, (well, if it's been off before) just leave the brackets in place, unbolt the bumper via the bumper bolts.
Had a skidplate, but removed it. Simple unbolt, remove operation, though IIRC, when pulling it down, it will hang up on the trailer hitch or something on that end. I just bent the mounting points on the skidplate a bit (easily bent back when in place I figure) and it dropped out.
Disconnect the ground and pink sending unit wires so they don't get ripped off when the tank drops.
Once all those are done, floorjack with a big board on it to spread the load, disconnect the fuel *fill* line/vent line for the fill neck, remove the nuts holding the gas tank straps tight in the back, and lower the tank down with the floorjack just until you can remove the fuel/evap/return lines from the sending unit.
Once those are off, lower until the jack is flat, slide tank off, and slide it out from under the truck.
Also might be easier to take the load off the suspension to get more clearance to work.