After much logging and some dyno time I have come to the conclusion that all 20776/20773 based tunes with the 2.5.5 version of TuneECU that I have ever worked with have an anomaly at 5800 RPM and higher.
As a result I am pulling every TuneECU tune I have made down, and advising all owners to seek out other means (PC-V, Dobeck, Tuneboy) of tuning their bikes.
The Long of it:
The TuneECU software allows you to adjust the RPM limit, however, the fuel cut is still active to a certain degree. The AFR from 5800+ swings very very lean (dangerously so), so it would hold a nice solid 12.8:1 or there about up to 5800, then swing into the 14 or 15 to 1 range, regardless of inputs into the fuel tables. My suspicion is the revlimit adjustment only moves the hard cut (full fuel cut) to the RPM you specify, and the soft cut is still in place at 5800.
The only way I was able to catch it was a dyno print out where the sensor was suspect. Then datalogged on the road in 4th and found the same issue, so its not a sensor malfunction, its the bike.
Tunes based on 20776 or 20773 have both yielded this anomaly, but tuneboy does not using the live tune, pretty definitively isolating the problem to TuneECU and not an anomaly with the 2014+ bikes, but the software specifically.