Fuel pressure problems

I have a 1973 Dart Swinger with a 440 Over the winter I up graded the fuel system starting with a new fuel tank,3/8 sending unit,3/8 aluminum fuel lines,all an fittings,performance mechanical fuel pump,fuel regulater with gauage.But the problem is when the motor compartment gets hot my fuel pressure drops from 6.5 to around 2 to 3 pounds at idle and idle is rough and when I shut it off it pops from the tail pipe,but when cold it seems fine! scratching my head any help would be great! Thanks Toy Snyder