replaced gas tank with one with same setup, now when engine runs under demand it loses preasure. i have a holley carb on a computer operated carb setup, but it was runing ok before th tank swap. still using mech fuel pump. i took fuel line off before mech pump, when engine was cranking fuel flowed but when engine started fuel stoped, this system has an intank pickup that is electric, and the mech fuel pump. why does pickup work when engine is cranking and stop when engine stops. its like fuel seems blocked when engine is runing.

 

Sounds like something has happened to the running power to the in-tank electric.