So I got about 15 hours before the same problem, air in the fuel filters. Since the fuel filters are the high point I'm guessing that I need to run a bleed, or return line off that housing as well. That or run an actual fuel pump around the lift pump to see if that is where the air is getting in. I just replaced the lift pump though, doesn't mean its not the problem, but it is brand new. I don't really see how the racor could be sucking air into the line, but I can see how it would happen, just can't be looking in there while we are running, fuel line was well above the outlet line on the racor when I checked. So that has me thinking it is a faulty lift pump. Anyway, I'll decide what to do later this week and keep this thread posted when i know more.