Im having a problem with my 99's fuel system. I started by installing a mechanical fuel pressure guage using one of the ports on top of the filter housing. With the stock lift pump I had around 10 psi at idle and no less than 6 at WOT. After a few weeks, the guage started reading a little lower but the truck was running fine. One day, it dropped to 3psi and I got worried. After a new fuel filter the guage showed 4psi. Not wanting to chance it, and already having a Holley Blue sitting on the shelf I ordered the Vulcan Big Line kit. After installing the kit I fired the truck up and only saw 5psi. Checked the lines for the fuel pressure guage and discovered air in the guage side of the isolator. I pulled the lines apart, replaced all the compression fittings, refilled the line as best as I could and reassembled everything. Fired it up now I have 11psi. Took the truck down the road and could only pull it down to 9psi so I thought maybe I was safe. When I started it today, it was a 4psi and eventually climbed to 10. What is going on with it? Is my guage messed up? My pump? I thought the Holley was rated at 14 or 15psi so isnt that what I should be seeing? If anyone has any ideas or has had a similar problem, I need help.