The regulator is on top of the fuel pump, to check it you need a fuel pressure tester obvioulsly. the pressure should hold after you turn the motor off. If it doesn't hold , then you need to isolate the regulator from the fuel rail, by pinching the rubber line after you get the pressure back up. If it holds that means you have no leaking injectors , and the problem is the regulator.

And I would also suggest you remove each connection one at a time for all the sensors and clean them and put compound on them.

 

I have almost the same exact issue. Run the truck every day and it starts fine. Let it go unstarted for a few days, and then it is very hard to start (seems to get worse the more days I let it sit) and then when it I do crank it over, it will catch here and there and not start. When I fight with it long enough and eventually can get it started, it then it spits and sputters (sounds almost like a backfire through the carb here and there, if it had one) and then finally "catches" and starts running normal and idling fine. I have put new gas in it and also used fuel water remover (wondering if that was the problem).

Did you ever find a solution for your truck? I am thinking maybe electrical for my truck also, since I live in a cold, rainy, humid area in the winter and maybe moisture is the problem. Just would like to know what fixed yours so I can try it first, before throwing a bunch of parts at it.

 

If I haven't driven the truck in a while I let the key sit on before I start it, it seems to help it start easier. I think it lets the fuel pump prime more before using the fuel that it doesn't have. lol