Don't get me started on the acoustics of a Ranger(a friend of mine has one)
One 15" with 600w could cause some seriuous hearing damage.

HOLY CRAP! I have the loudest system at my High School. Some of the other kids have 2 12'*, but they don't have the power running to their subs that I do to my 15. It'* sweet as hell. Get'* a lot of looks too.

profile overates their amps that amp is only pushing abour 200-250 watts max as far as the box goes if u want a wider freaquency range go with sealed, which will also increase power, by the way, but if u want it to get real loud over a certain band of freaquencies go with ported; either way get a new amp and dont be suprised if it blows soon

i maybe wrong but i "heard" that the bigger the speaker the lower the effiency? most reputable are 12s as far as amps pick one tha matchs the sub rms wise not a peak rms is constent peak can only be handle for a short period of time

one more thing the way you have your system set up its going to louder than a car with a trunk cuz you are useing the cab as a box in a way? its hard to explain? but a car with a hatch would be simialar to your truck but i could be wrong does anybody know what im trying to say?