Good point... the OP has changed pumps, and checked pressure, but that pressure check is likely at idle and that does not say anything whatsover about that pressure being maintained at the top end under max flow conditions.. And, the OP checked open pump flow into a container, BUT, that says nothing about flow into back pressure; pumps with poorly functioning check valves with have their flow drop radically or to nothing when back pressure is applied.
So, while those are good checks to do, they are not 100% conclusive checks that the pump & fuel system are delivering fuel properly at max flow conditions.
The easiest way to know is the rig up a fuel pressure gauge that can be observed when running hard. Just be safe when doing this.
OP, I see you put in a new pump of adequate specifications. Did you change the regulator? And while the free flow test says the pickup is good, any way the cell pickup, or any foam blocks, are moving around and getting masked under acceleration?
