Glow plug relay
 

Would a bad glow plug relay cause a truck not to start at all or cause it to hard start??

Sure check for power at the glow plugs-these need glow help even in warm weather.

I drove the truck Friday night. Got in it Saturday mornings, wouldn't start. I tried a few things and nothing. Hooked the battery charger up for a couple hours. Messed with it some more. Finally I said what the heck and open the bleeder on top of the fuel filter cap, turned over a couple times and started right up. Had to open it 2 more times Saturday to get it to start. Bad ip, leaking injectors? There is no cracks anywhere in any lines, nothing is wet.

Check closer under the filter housing-sounds like fuel is leaking from the water in fuel sensor or fuel heater o-rings in the filter housing letting air in.

Leaks between the LP and the fuel level in the tank tend not to leak fuel but suck air since they are under suction rather than pressure.