This might be a long shot here but have you checked the return line pressure ?
I know a TBI will act that way if the return line is restricted ..
Basically what happens is as the engine reves , more fuel is dumped but because of the restriction , internal pressure is raised . Basically causing a loss in power and slow climb on the RPM range
Maybe on of the other folks here to tell you what the return line pressure should be for a TPI .
I know with a TBI it should be zero .
If its not all kinds of odd things happen ranging from rich mix , O2 codes , galloping
Might be worth a look