2012 Mack CXU613 fuel issues

I am having issues finding where the air is getting in on a 2012 Mack CXU613 MP8. Any tips or advice?
I changed the fuel filter housing unit and fuel pump. Now I can’t get the truck to stay on.
Prior to changing the filter housing. I was losing prime, however I would prime the truck and the truck would work fine. Since changing the Filter housing and fuel pump. Truck has been sucking up air and won’t stay on!

 

Truck got around 630k but had an overhaul done at around 500k. No codes for fuel. Only code is a FMI 645-647. Not sure if cups had been replaced when the overhaul was done

 

Rebuild was done before I bought the truck around a year or so back.