Truck Repair: 95 dodge cummins 12v takes awhile to start after sitting, drain check valve, dodge cummins

Question
i have a 95 dodge diesel auto 12v diesel.  thing runs great as always but now in the last two weeks if i let it sit for more then a day i must use gas pedal and once started it runs like its on a couple cylinders unless i have my foot on gas above 1000 rpm for about 30secs then all is good.  i was thinking of replacing the fuel filter first but doubt that will cure the problem.  i was thinking problem is either bad lift pump or actual fuel pump. any help is appreciated.

Answer
Most of the time a lift pump & fuel drain check valve will fix that problem.The overflow valve is located on the inside of the fuel pump right in the frt.Takes a 3/4 wrench to remove it & it will barely clear the head where they machined it for that reason.It also has two seal washers on it.But surely one of the check valves(either in the transfer pump or overflow valve) are leaking letting it drain back to the tank.But which one it is is a guess.