take the hose off the cooler and reroute it to the block-no parts needed----
a possibility is that the cooler is cooling the
oil to the point that it thickens and won't flow anymore so you might try blocking the airflow to it and not running at high rpm until
oil is over 200*
It could also be that the way you have your pressure guage plumbed that you have a venture effect past it causing a psi drop at that rpm
AND-----you could have all the
oil pumped outta the pan by that rpm with the HIGH volume pump and it just hasn't returned to the sump--------