seat belt light will go off if you wear your seat belt... lol
you realize if you get in a wreck in that truck with no seat belt on, that airbag is going to snap your neck like a twig... they come out with explosive force...inflate and deflate before you realize wtf just happened...
anyway, you will void your warranty if you tune the truck or modify it in any way.
assuming you don't give a rats *** about your warranty: delete the DPF in the exhaust, its like a giant cork in the exhaust... next delete the EGR valve. its plugging up your intake and turbo with soot. those two deletes alone will gain you 5mpg. no joke. but warranty will be out the window and truck wont pass emissions.
now for power: you will need a set of gauges: EGT, Boost, trans temp, rail pressure.
once you get those, next is building the trans...torque converter and valve body will go a ways, or if you want serious power just ditch the trans for a fully built trans so you can do it right the first time...
then for electronic power you can get either a smarty programmer, or EFILive. both will boost your power a good 200hp to the rear wheels. if you want more than that, you can do injector nozzles and throw a S480 under your VGT for compound twin turbos. you will need head studs, o-rings in the head, and upgraded push rods and valve springs for running twins on your truck. always do supporting mods first or you WILL break your truck. (I learned a lot of it the hard way and it cost me a lot more money than it had to...)