My B&M fuel pressure gauge reads around 45 psi after shutting the engine off but overnight it drops to 0 - 5 psi. I am thinking its either a bad pump assembly (valve?), leaky injector seal or bad gas cap (I got an aftermarket one)...

I do plan on fixing this soon but will this issue affect driveability or acceleration?

 

My Aeromotive fpr drops to zero after 15sec with the key off, nothing to worry about; As long as your afr's look good with the engine running.