[Accelo]

Should run great with the stock motor and the stock tune.
There are speedometer correction businesses in the larger metro areas.
They service electronic and manual controlled systems.
Or even send the ECM back, to the original guys, to have the ratio corrected.
However, you mentioned it is running / driving great.
Is you speedometer correct? Is the source cable driven or electronic?
Are the shift points where you like them?
Not sure you need to do anything but enjoy the ride?
The proof is in the function!
Cheers