14L Detroit loss of power and loosing prime

Hey guys I have a problem that has been really messing with me. Truck is a 2004 Freightliner Columbia with a 14L first of all truck is loosing primer over night. take 15-30 seconds to turn of just keeps cranking, I have read that this could be a Fuel Check Valve? Now I also have another issue the truck will loose acceleration while driving it pedal will sink to floor and RPMs will go down the thing is it happens so randomly can go days with out doing it and than next day will do it as soon as it goes down the road other days will work fine than after 5-6hrs of driving will start doing it. I have changed out Fuel Filters, Check Valve at fuel filter housing and fuel tank air vent can the Fuel Check Valve behind the head be causing this? anything helps.

 

Hey guys sorry forgot to mention I am not getting any check engine light.

 

Yes Davco fuel water seperator, I changed out the plastic ball last week. I will try this thanks!