KW Detroit 60 power fall off?

My rig is a 1999 KW W900 with a Detroit 60 (12.7) and DDEC-IV control.
I had it custom flashed to provide 550HP and 1850 ft/lbs.

It fixed one problem but not another:

1. I have rapid ####### acceleration and great pull power.
2. I still have a power fall off I can feel at 76mph.

..when I reach 76 mph in 8over, I am doing about 1500RPM - which I think its top HP?
she will still continue to accelerate but like an old lady using one of those 4 post walkers with cut tennis balls on the bottom.

Since the problem was present before the ECM flash, I can't blame that.
The parameters when all printed out - do not indicate any restriction of any kind and no speed limiter is present.

Any thoughts on what to do to deal with this, presuming I can?