Fuel pressure problems

I had the same exact problem.
I had good fuel pressure at start up.
As the motor reached running temp my fuel pressure would drop to 4.5
I did everything to protect line from getting hot to avoid line lock.
I covered all bases far as insulating line from heat as well as phenolic carb spacer.
I finally broke down and installed a Griffin radiator and used a fan shroud.
Fan shroud is a must to direct the air directly on the motor.
I did not change anything else and have not had that problem since.
The entire car runs much cooler inside the interior car and a big difference under the hood.