Before dropping the tank, check for 'active' current out of the inertia, (remember its timed and only hot for a few seconds on a key cycle) and at the tank module connector. If so,, have a helper cycle the key to 'ON' as you whack the bottom of the tank 'firmly' with the flat of your hand. Sometimes a faulty pump will run on impact applied
I included the pump schematic....

 

This is a rather lengthy update of my findings yesterday after going over everything again. Battery checks good and is at 12.3 v.
Power to the inertia switch is 11.5v. With key on 11.3v out of inertia switch. Cycled key on numerous times no fuel pressure registered. Tried starting-no luck. Misted in minimal starting fluid and started right up with fuel pressure jumping to 34psi and then leveling out at 30psi. Ran thru several rpm's including quick hi-rev and release. Fuel pressure did not go over 34psi or under 30psi. Engine ran and responded smoothly Did not drive the truck. Shut-off and fuel pressure immediately dropped to 20psi then climbed to 36psi within 5 minutes. Pressure slowly dropped to 20psi over 2 hours then continued down to about 5psi over the next 2 hours. At this point tried starting truck and started right up. Cycled thru rpm's as before with the same results. Shut-off and relieved all pressure at the gauge relief port. Would not restart without starting fluid again.
Any opinions or advice?

 

This is only an opinion AND may not be worth very much, but lets look at what might be happening.

When you shut the engine down, the fuel system is supposed to hold the pressure, period !
What can contribute to pressure loss,
1. -.Defective check valve in fuel pump module in the tank , remedy,, replace entire module assy , cost a few bucks , so expect that.
2. Fuel pressure regulator leaking internally allowing fuel pressure to drop off.
3. Possible leaking line under vehicle
4. One injector leaking and allowing pressure to drop off , Clue might be present in motor oil with dilution and strong gasoline odor on dipstick.
What happens when you turn the key on, do you hear the fuel pump run for the usual 2-3 seconds? If not, could be PCM problem.
If you turn the key on, wait a few seconds then off ,and repeat the procedure one or two more times, will it start then?

 

Hanky asks if you can hear the pump running a key cycle. Y/N?
If you’ve verified current out of the inertia, and/or at the tank module connector, chances are the pump is failing. Even if the pressure bleeds off internally after a cold soak, cycling the key ON a few times would/should build the fuel pressure, and one of the reasons the question is asked.
The PCM controls the fuel pump relay only, not the ground or power distribution of the pump motor. So if a test power is introduced to the inertia OUT, the FP should run “continuous”. If not, I’d suspect the pump, more so if still OE. You can also apply a test current at the module connector to rule out anything ahead of the pump module as far as diagnostic.
Did you attempt cycling the key ON while applying a hardy hand impact to the tank bottom?? Many times the pump will start. Then,, after the key is shut off, the pump have the same issues. The reason the pump has a “timed” run in a start/crank, is to aid in pressurizing the system....