Ebay GT45 + 5.9 Magnum + E85 blow thru

Ok looked back in your thread and if your fpr is still connected by vacuum to the throttle body you need to change that. The boost reference should be coming from your carb hat directly to the fpr.
Yes. Boost ref goes from carb hat to FPR, indirectly through a distro block. I've tested it, and the FPR get's boost signal no problem.