Losing fuel pressure on new setup

I just finished changing out the whole drivetrain in my 72 duster. I have a new 3/8 pickup, 3/8 hard line (aluminum) with the fuel filter roughly by the passenger floor. Running a carter m6270 if i remember right and a holley dead head style regulator with -6AN from the pump to the carb. Holley 750 dp with a proform main body, carb is proven and worked great last year.

So heres what its doing: it will start fine once fuel is in the bowls. I will have good pressure (6.5psi) at the carb and after about 15 mintues of driving it will be down to 2psi hardly registering on the gauge and the engine starves and dies.

I tried eliminating the regulator to see if that was the issue and it started off at 8.5 psi and fell down to 2 just like before but it seemed to last a little longer. Then i thought possibly vapor lock but it was only 65 degrees out and i hardly drove it. Also i insulated the lines whenever they get close to the header. I have a stock pump i can put on to rule out the pump being faulty. What do you guys think? Everything is new and this is a pretty inconvenient problem being consistantly stranded. Feeding 500 hp 390 and open to any suggestions. I would like to keep as much of my setup the same as possible. Thanks for any input!