had the injection pump and lift pump replaced about 2 years ago. have a guage on the filter to measure the fuel pressure. my question is when you turn the key on, but not start the truck it (the guage) reads about 12-15psi, but once the lift pump shuts off it drops to 0. should it be holding some sort of pressure? and also the longer you wait to start the truck after the lift pump shuts off the more it cranks to start. should i get another lift pump? there only about $100 verses $500-800 for one of those FASS pumps.  

if i were you get a fass hpfp lift pump, they run about 400 bucks, some are even cheaper such as the raptor pump from airdog which runs about 350 bucks.  personally, i done the same thing, kept replacing the stock pump with a stock pump, after replacing 3 pumps in 6months and 8000 miles, i said enough was enough and switched to the fass, now 110000 miles later and 450 hp, not a single problem, and thats with my factory  VP injection pump!  I see 15 psi at WOT and at start up 22 psi, no problems starting at all, anytime you see the pressure drop below 7 psi, youre in trouble.  

Key on pressure 12-15 lbs then dropping off till the motor is started is normal. Listen to Dukeboy and get an aftermarket lift pump...it's money in the bank!