Falling fuel pressure

What type of fuel pressure gauge are we talking about? Liquid filled fuel gauges will read lower pressures as the engine compartment heats up.

Straight from the "notes" section on a Summit fuel gauge...

"Liquid filled pressure gauge readings will change as ambient (under hood) temperature changes. A liquid filled gauge compares line pressure to the pressure inside the gauge case. A change in ambient temperature can cause case pressure to change as much as 7-12 psi. As a result, gauge readings can fluctuate from 40 psi cold to as little as 28 psi hot."

Summit Racing® Fuel Pressure Gauges SUM-800115

Now, for some reason they're talking about EFI type fuel pressures in their example, but it doesn't really matter. If the gauge shows 5psi cold, and drops to 3 psi when everything is heated up, it could be completely due to the way the gauge reads the pressure, and not an actual drop in pressure.