Truck Repair: hard starting, fuel pressure regulator, fs1000

Question
2004,ism. Very hard to start, gotten worse, fuel solenoid has power, fuel filter is new, batteries new , turn over fast, suction line not cracked,fuel line seals ok, the fitting on top of the fuel filter is apparently for checking the pump gears suction, only get 2 " of mercury, but can't tell if that is really true reading or not, no smoke out of the exhaustwhile trying to start. So any suggestion would be appreciated. THANKS !  

Answer
I would check to see if it has a tube in the fuel filter(FS1000 or 1001).Check fuel pressure while cranking.Needs atleast 40PSI to fire up.Possible fuel pressure regulator sticking or leaking back if low.You will register a vacuum if just air & not fuel.