It's definitely a starvation problem if it runs on Brakleen, and if you're seeing pressure drop at the tank then chances are it's a tired or binding pump motor that's losing torque and speed when it gets warm. It won't be a blockage because you'd see rising pressure and not falling. I don't recall if D21's had a return-type regulator, if so it's possible that's causing a drop. You can check that easily by temporarily pinching off the return line to see if its disposition improves. Otherwise, just check voltage drop on the power and ground wiring to make sure that isn't the issue before condemning the pump. If your pump power is good then it sounds like a bad pump is the correct diagnosis.Was able to get the bed off and test it by the fuel pump and was getting about 40 fuel pressure before it dropped.