Hello!
I just wanted to share my experience regarding fuel pressure drop after warming up my car.

I installed a new Walbro 450 fuel pump and rewired everything with new relay. I set it up @35 psi and it would drop to 30 psi after warm up. I checked the voltage at all ends and everything was fine. After doing some research I found a threat about using a liquid filled fuel gauge which causes the reading to fluctuate up to 1 pound per each 30 degrees of temp. I had a Marshalls liquid filled gauge that seemed to be the problem.

So, I went to Home Depot and purchased an air compressor gauge and problem solved.

I hope this helps someone that has the same problem.