I personally don't like the liquid filled gauges but could care less what others want to use---a pressure guage will read the pressure in the line and will only be effected by the outside atmospheric pressure------- the dips/swings of a gauges needle is a result of the IMPULSES in pressure-maybe effected by pump and/or regulater action. The larger Holley type carbs have larger diameter needle/seat assemblies and so are more sensitive to line pressure leaking past-

The fuel system with a BIG pump and a return line circulates the fuel in and out of the tank causing under vehicle heat to warm up the entire load to whatever temp the under side of car is seeing.

In this guys case he could shut off electric pump and run car til it quits--------also check tank temp after a road trip to see what the fluid temp rises-