Ok for about a week now I've been having some issues with truck starting. Plenty of power but not firing. Last time I had this issue ended up being the inertia switch. After being replaced boom good to go for about 6 months.

Now, Same thing, tried resetting inertia switch, nothing
Check the fuel pressure 65 psi boom starts right up.
Sitting about 3 days again same thing. Inertia switch is good but this time when cranking, it sounds like its skipping a beat. Just replaced camshaft position sensor, nothing. Go to check fuel pressure and after hooking up gauge, key on, 65 psi and cranks right up.

Now, what causes my truck to start everytime after pressing Schrader valve for fuel check? I'm at a loss and not sure where to go.
Thanks for any help in advance.