[Henry Schmidt]

I would suspect ignition or MFI pump timing.
We recently had an MFI engine that was making us crazy. We went through a plethora of engine tune up possibilities and then did it again without success.
After literally months of anguish we took the engine out to discover that the MFI drive pulley on the cam had come loose and the mounting holes had gotten oblong so the pump timing was constantly changing.
This engine had a high rpm miss but your problem (lack of high rpm power) may be pump timing.
Good luck