90 - Running out of breath at 5000 - No Codes

[dondon]

Trying to figure out why my 90 5800 mile ZR1 (new owner) completely runs out of steam at 5000 RPM, it doesn't pull particularly hard to that point and really badly from 4000 RPM.

Background:
I previously had a code 61 - which I ended up replacing the solenoid, vacuum canister and secondary plastic piping. I checked the actuators and both openned quite easily. The car no longer throws a 61. When reassembling the solenoid had an extra nipple which I plugged (don't do this). which led to a hard code 56. Upon removing the plug, the 56 has gone away. The only modification that the car has is a Haibeck chip which is slightly detuned to handle the 90 Octane ethanol free gasoline.

I'm a bit of an odd case judging by other forum members in that I have original injectors, I don't believe the car should have injector problems as it has always run ethanol free gas. The fuel I'm using currently is 90 Octane Ethanol Free, as sold at a local Sonoco station.

Anyway, at this point I'm not getting any codes coming back. I've attached a datalog from datamaster. Its short and hopefully it tells enough of a story. Anyway, any assistance would be greatly appreciated. I haven't owned the car since new, so I can't say I know what a clean pull feels like, but as it stands the car quite often feels like it hesitates, and even at times it feels as though spark is cut momentarily then the car starts to pull again.

Any thoughts would be greatly appreciated.