Let's see...replaced them about every 80k in my 99 (stock) just to be sure (only had one die on me)...dad has replaced 3 in his 99 truck...same deal, replace them at 80k miles to be safe...he's at 225k with the original VP44...I was at 201k on my original IP. We only had gauges in the filter housings...they were always at least 12psi at idle.
I changed to a FASS at 58k on my 04.5...keeping my factory fuel bowl mounted LP on as a backup to the FASS...didn't have a gauge on the factory, but the FASS was 25ps when I first put it oni...I changed the spring to a 13psi...now I got a solid 12psi at the CP3.
Of all the options I looked at the FASS was the best choice for me...the RASP needed to much extra plumbing and still uses the factory LP to start/prime. It was also apparent they eat belts. The AirDog was too much $$$..for getting something almost the same as a FASS. The stanadyne used proprietary filters (reverse flow) and I believe they state it is only a pusher pump (not to be used alone). The BD kit uses the same junk Carter pump...I wouldn't have replaced a Carter with another Carter. The Holley blues/blacks have mixed results (some last for a couple weeks, others last a good long time). The car-grade aeromotives won't stand up to diesel...unless you buy the $400 marine (diesel) unit...I only paid $470 for my FASS.
I think a lot of guys have figured it out...it is volume, not pressure that you need...getting rid of the factory fuel delivery lines is one of the best things to do (it also takes load off the LP too which should give longer life)...I can tell you my mileage and power are both up after the FASS install...my biggest restriction is the in tank pickup assembly since the FASS uses 3/8" line from the pump to the CP3...now that I own one, I couldn't think of getting anything else...most likely get a FASS for the old man's truck this summer.
steved