Youll get more help there rather then this
website. my username on there is M5B6L
To add to the help you have already gotten. Dont get a fass, get an airdog aka pureflow diesel.com (life time warrenty and cheaper). And get a fuel pressure ( 0-30psi), boost psi and exhaust temp gauge when you do get that installed. Most likely your vp is on its last leg. Check for codes my turning your key forward before start position and off 3 times. Your odometer will flash and give off a few P_ _ _ codes.
Do you have any programmer or chip on the truck? or did the previous owner?