So normally my fuel pressure gauge on my aeromotive fpr seems to read about 44 psi or so at idle. I realized today that it is only around 40 now. Is this normal for the base fuel pressure to move around slightly like this?

 

Base pressure would be whatever the regulator maintains unplugged from the manifold. With the regulator connected to the manifold fuel pressure should vary with manifold pressure. So, if vacuum increases fuel pressure decreases, if boost increases fuel pressure increases,

There is one exception: the ECU will connect the regulator to atmospheric pressure at hot start by way of the fuel pressure solenoid.