I have upgraded my deck and door speakers and the factory sub but I'm not happy with the sub and am curently looking for a better set up. I have a nice pioneer deck, JBL components in the front, and JBL 2way in the back. The sub is a JL audio W1 series 12" in a small slim box that I'm just able to squezz under the rear seat. It doesnt' sound bad but the base is just not loud enough to keep up with the rest of the system. I have looked at about everything there is for a f150 and the best thing I have seen is the JL stealthboxes they make custom. They are expensive but it seems like they are the best option for me anyways. If you get a custom box for under the seat you will have to get a riser set up if you want 12's other wise you can get 10's and just remove the jack. You can only fit shallow mount subs in most of these boxes as well which don't sound as good as regular subs. The stealthboxes are $750 for the f150 and it comes with a w3 series 10" loaded in the ported fiberglass box. Add the amp and your looking at a grand or so. Imo anything more than 12's is overkill unless you are doing competitions. If and when I upgrade my sub I will post a review and let you know how it sounds.