fuel pressure dropping over time

The braided lines will do a pretty good job of keeping the heat away. I would suspect the regulator is funky, or the fuel pump is weak. Even if your parts are new, it can happen. I would bypass the regulator temporarily and see what that does for you.
Not sure if I can bypass it (at least not easily)
But I bet I could "gut" it and run it as an open T

I'll see if cleaning the filter helped, and if not, I'll try that