re: Trading in my F150, need help.

I was at a GMC dealership yesterday and they all have manufacturer discounts of $6250 right now on the 2015s

ICS, if you're dead set on a 6.4, you will most definitely want the following:

Updated radiator and hoses
external oil filter
updated front cover
complete cooling system flush and red ELC(I used cummins flush stuff)
should put in new t-stats when you do that
check 4wd hubs

If you are tuning it:
Tuner(not turned all of the way up)
full exhaust
intake
new oil cooler
EGR/DPF/DOC deletes
can't stress how important studs are

That's all I can think of off of the top of my head, but for just parts, that should be on the high side of $5k. Labor on a diesel is $100/hr