I've been (or was I should say) using an Aeromotive pump and one of their bypass regulators. I also have a fuel log instead of 2 separate lines to feed the carb. No matter when it was, the pressure was locked at 8 psi where I set it and never moved whether it was first thing in the morning, hot after driving, under full throttle, etc. I had one single feed line to the pump (going with 2 now) and all line, feed and return, are -8. I don't think your feed or return lines are your problem. Gotta be either pump or regulator.