problem with Davco fuel filter sys, maybe?

I have had problems with the davco filling up too fast due to water,contaminants in fuel e.t.c. but for the first time ever. my filter is not showing any fuel. after 1000 miles no fuel in sight. it usually starts to fill within 100 miles, then slowly climbs. I took cover, collar, everything off put new seals in & refilled with fuel. got 1500 more miles. still no fuel in sight. truck runs fine. no air that I can tell anywhere in the sys to create this. just wondering if it is anything to worry about? I can bump the bottom of the davco & get the fuel to splash up in the dome, so I know the fuel is there.

 

o.k thanks for the replies. I use the donaldosn filter same as the last 15 years. with my route. I fuel every day with about 1/2 full on tanks when I fuel up. I do not have any tank shut off's

 

O.K. still no fuel visible in the dome? with the bio fuel I would have to change no later than 8,000 miles. tried another filter, made sure all seals intact. is there any way for the fuel to get from the inlet line to the outlet line without going thru the filter? from what I see the fuel comes in from the inlet hose, goes up thru the middle of filter, than out the sides into the outlet hose, the 380 has no other parts that I can see that would affect this.it is just a metal cylinder. I do have a pre heater, if that could cause this. I just do not believe I am getting that pure of fuel. it has never done this, ever.