Many drivability diagnoses require measuring the fuel pressure, both while sitting still and under drving conditions. The following is one method of providing such measurements.
1. 60psi plumbing pressure gauge, round face style, bottom outlet, from any good hardware or plumbing supply house
2. barbed brass tee sized to fit rubber FI fuel line from steel hard line to fuel rail.
3. Schrader valve, like a tire valve. Hardware store or catalog like McMaster Carr or similar.
4, air line fitting to scres onto a schrader valve.
5. about 2' of FI fuel line.
6. Female pipe thread x barbed nipple brass fitting sized to fuel line and pressure gauge outlet.
7. schrader valve cap with fuel resistant oring inserted sized to friction fit in the cap interior for a seal. Bicycle shop or hardware store or tire store. You want a metal cap.
8. FI quality hose clamps, 6 or 12, depending on whether you want to double clamp.
Cut the rubber fuel line from firewall to fuel rail, pressure side that connects to the rear pside of the fuel rail. Install the barbed tee with hose clamps, and connect about 8" of new fuel line to the tee side outlet. Install the schrader valve in the other end of that hose. Install the pressure gauge and the schrader valve female air line fitting to each end of the rest of the hose with clamps. For normal unmonitored use, screw the schrader valve cap onto the schrader valve. This is a safety cap in case the schrader valve develops a leak.
To test fuel pressure, remove the safety cap and screw the tire fill air line fitting to the schreader valve to sealing pressure. Turn the switch to on (NOT start), and the fuel pump should run to pressureize the rail. You have enough hose to tape the gauge to the windshield so you can monitor from the driver's seat. Before starting the truck, inspect the connections for leaks. Observe the gauge and see if the pressure drops quickly (leaking FPR). Now crank the truck and note pressure. THis should (I think) be 46pai. Put the truck thru a drive cycle and look for any change in pressure, especially drops under heavy accel.