The lift pump referances Oil pressure to run....no oil pressure, it quits running. SOOO....the sending unit that its using could be bad.....also the lift pump could be bad. ALSO sounds like you have a bad vaccum pump/line to the Waist Gaite. Go mechanical conversion....it takes that issue out for good. Best thing to do is see if you are getting fuel pressure....if not...test for power at the lift pump on the rail.....if not....might need an OPSU. BUT i have VERY limited knowledge on this truck..i have worked on a few........not the easiest to wrench on.....what part of Texas....i used to live in Gainesville until last month......
Talk to www.Heathdiesel.com
Talk to www.Heathdiesel.com