I have a 1974 455 olds with red inline Holley fuel pump (new) . Holley 850 double pumper. Runs for a couple min and loses fuel pressure and runs out of gas when gas tanks  are clean and full. New lines all the way through. new fuel filter? Any ideas what the issue could be?

If you can't find anything wrong with what your Mom States:

 Disconnect the electric pump all together. Then see how it runs with just a good mechanical pump.
 So many good high quality, high gpm mechanical pumps available from both Mondello sites now , I question the need for electric.
Just my 2 cents however. Nice-looking float. And welcome to the site.

are your vents clogged? remove fuel cap to test.. cheapest and easiest checks first