new to forum,2003 duramax losing prime

[LJ1962]

My 2003 GMC duramax loses prime sitting overnight and sometimes in a few hrs.If i park on a slope with the nose down, it usually will start without pumping the primer on the fuel head. I replaced the seals in the filter head and it worked great for 3 days , so i thought that was the problem, but then it was back to the same old thing.
I have a nicktane adapter with a new cat filter. Replaced the fuel lines from the engine back to the tank lines(did not replace the short lines going into the tank).Replaced the lines going from the fuel filter head. Replaced the 2 small low pressure lines under the intake. The truck will usually start right up, run 5 seconds then die. If i prime it with the filter head pump , it will start and run ok. Dont know if its related , but after i prime and start it , it surges slightly while idling, dont notice the surge later in the day after i've run it awhile.Truck has 230k miles, injectors and head gaskets replaced at 168k.
No evidence now of leaks, any ideas on what to try next?, its driving me nuts. been working on this off and on since April.

[rapidoxidationman]

A lift pump will take care of vacuum side fuel leaks and would bypass the problem of air getting in (by pushing fuel out, thusly making leaks visible), but my money is on a cracked filter head. Your rebuild/reseal only working for a few days tends to confirm this, in my opinion (which is worth exactly what you paid for it).

Just for comparison, I replaced the fuel filter head on my '05 at
...checks maintenance record...
225,305 miles back in December of 2016.

[More Power]

Diesel fuel caps are cheap. They have a 2-way pressure/vacuum relief valve. A faulty relief valve can cause these sorts of problems or make an o-ring seal or some other type of leak much worse. Vacuum can sometimes pull air into a borderline fuel line fitting but pressure can't find its way out due to the way seals and O-rings work.

This time of year, depending on where you live, large temperature swings in ambient temperature throughout a 24-hour day can act on the fuel in your truck's tank to produce pressure during the day and vacuum during the night. It's amazing how much pressure/vacuum can result from a full tank of fuel sitting through a 24 hour period - and a high to low temperature swing.

[Kennedy]

Lift pump first. I have yet to see a "cracked filter head" only leaking orings. Furthermore I have only ever seen leaks of air into non lift pump trucks. Those with lift pumps do not leak out fuel.

And put the stock filter back on. It is a multi layer unit and as good or better than the overrated Cat unit. If you want to do something positive add another filter.

[chessy56]

+1 on the lift pump recommendation. There's a bunch of them out there but I used one of Kennedy's pumps on my former LB7. Took care of my prime problems and fully used the available filtration area of my filters.