I wrote a few months ago that I has solved the high rpm misfire.
I was wrong. But I am not confident I have found a complete solution to the problem.
It now looks like the problem was caused by the wiring, specifically the wiring being packed to tightly under the dashboard and/or resting on top of the original ECU.
Removing the ECU to the floor on the passenger side seems to have cured all the issues. The engine now pulls strongly to the redline consistently.
I have had a number of problems with the AEM FIC8 since we installed it and without exception, all the problems have been done to the installation not being 100%.
The AEM FIC is hardwired into many of the functions of the standard ECU. If the connections are not 100% correct you will have problems.
As I wrote earlier we were using cheap plastic covered crimp connectors. There are not of sufficient quality.
You need crimps with 2 pinch points. One to hold the wire and the sleeve and another crimp to hold the bare wire. This is the only way you can connect the FIC. (See image)