Air In Fuel System
 

We have a 2007 3500 GMC Duramax, and when it sits for an hour or so the fuel filter is dry and full of air. We have replaced fuel line, pressure tested the line, we have tested the fuel filter and the check is working. Also, we have bipassed the fuel filter, and it did not help. We can not figure out what the problem is. Does anyone have any ideas?

is their any fuel on the ground? i know stupid ??, but that is a lot of fuel going somewhere and is the lines at the tank OK or the fuel cooler, put a 6.5 lift pump on they are real inexpensive and the truck will like it plus it might help you find a leak that vacume from cp3 is drawing air

common problem areas:

-bleader screw on filter housing. most notorious for issues, even if it looks fine it can still be at fault. try Teflon tape to see of it is the problem and then replace it if it is. ebay has aluminum ones
-primer bulb seals. can get a rebuild kit on ebay cheap.
-hairline crack in filter housing
-water in filter sensor plastic part on bottom of filter cracking
-any of the lines after the filter
-check valve inside filter housing. removing filter you can see it in the center of the housing at the bottom. it is a plastic ball held with a spring. apply a few psi to the output line on the housing and see if it holds