isx will not start cranking low fuel pressure

[Geared_Cortex]

Hi , I just wanna update this thread with my personal experience so it maybe helps someone having the same issue. So it happened the first cold day of the winter here in Canada. I tried starting the truck and it was cranking slowly with 4 brand new Cummins batteries I had put in like 1 week before , it ended up dying and giving me the low fuel pressure code 94/18 . So I tried starting it with booster packs and batterie charger but no luck. Drained the water in davco still nothing. So I started investigating and found the very well hidden lift pump fuse that was blown. After changing it the lift pump started working but was sounding funny and of course no start .So I changed the filters in case it was that but still no start . So I came here to read on the subject like I always do and ended up on this thread. So after reading this I hooked up insite to see what was the fuel pressure when the fault code came on and it was 64 psi so I assumed I had a bad gear pump especially after reading that they just go bad without any warning. But I still was hoping it was a stuck drain back valve. So I dismounted the Ifsm and the lift pump and the valve looked good , checked if fuel shut off valve
was working and it was fine, changed the seals on it just because I was there already and cleaned everything up . Powered the lift pump and it sounded like it was pumping but no start and insite telling me 43psi while cranking . So tried poking the compuchek fittings with a screwdriver I had nothing coming out . So I knew at that point that my problem looked like a gear pump but it was just the lift pump not providing fuel to the gear pump to build any pressure especially after I had the system unprimed by changing the filters . So after I put on the new lift pump I still couldn't start the engine even with insite telling me that the pressure at key on was now 30 psi and while cranking it was 150 psi . I was really confused. Started looking for electrical problems and ecm related stuff but couldn't find anything . Cranked the truck maybe 30 times. Ended up calling a mobile mecanique to come fix it . While waiting for the guy chilling with my dad , I said to him come crank the truck for me I wanna try one last time but with ether this time. To my surprise the truck started. It was rough at first but after a few minutes it was back to normal and been starting like a charm now. So my reason for writing a novel about this is just to give someone else that could have the same issue a chance to maybe see something similar there experiencing and not end up spending on unnecessary parts and labor that could have been as simple as just some air in the system that is stubborn to come out.
Correct me if I'm wrong please. I wanna learn as much as possible.