Power cutting out at 5500rpm

[KzooMuscle]

I added nitrous to my setup over the summer. When I brought it to get tuned, we started with a 100 dry shot (easy install, and tune). The car was not taking it and it was cutting in and out - the graph was all over the place. My tuner thought it could be the ignition, apparently SN95's ignitions are prone to being weaker to newer models. So we tried a 75 shot, the car did better after some dialing in, but power would drop at 5500rpms, resulted in going from 669 to 697, but the tq was more noticeable going from 590 to 692. Again, my tuner was confused, and suggested this time it could be the converter coming loose on the dyno. This is the same guy that built my motor along with hundreds of other similar setups like mine, so it comes to a shock and it was quite upsetting to me that he could not pin point what it could be. He "reassured" me that the converter unlocking would not be a driving in the real world concern and the nitrous would work as it should, but it should had stayed lock on the dyno, that how their dyno program works automatically. I've spoken to a few of my friends about this and we are all scratching our heads as to how to perceive this experience. It is surprising that an engine builder and tuner with his experience would not be able to diagnose something like this, AND not be able to suggest a solution. He had no answer to the ignition issue, but the fact he does not like MSD and there really isn't another alternative out there to help me.

Can someone else shed some light on this? And/or give me suggestions what could be happening? I tried spraying the car at the track a month later and it would not engage there either, and I had 900psi in it - I know, not ideal so I am hoping that is the cause but otherwise, I am at a loss with this.