383 MAG MPI Missing from 2200-2800 RPM

I have almost 130 hours now on this engine, and a continuing problem is very noticable missing from 2200-2800 rpm.
This does not affect cruise, but of course wakeboarding and kneeboarding is right in this RPM range.
The boat is 21' and weighs about 2600 lbs empty.
The drive is a 1.47 Alpha Gen II and the prop is an SS HighFive 21".
The 383 is supposed to be used only with the Bravo drive, but all seems well running with the Alpha.
I think the mixture is too lean in the troublesome RPM range, and I want to try to get it reflashed with a mixture table that enrichens the mixture in this range.
Anyone have any ideas on who could do this?
I plan to phone Merc service and start there, but otherwise I am not sure where to go.

Thanks,
Rod

What you want is a custom tuner...who to see will be determined by the ECU used on your engine. Do a www search for MEFI custom tune to see what's available...

UPDATE:
I had a lengthy chat yesterday with dean and Todd at Mercruiser service.
They were very interested in my problem, and had lots of advice on what to check.
The feeling is that there is something electrical that is vibrating in this rpm range, and causing short duration power loss to the ECM which in turn is causing lack of spark for various cylinders.
The most suspect items they suggest checking are the 50 amp breaker, the key switch, and the 10 pin harness plug connections.
They also suggest checking the fuel rail pressure to make sure it is on spec in the critical rpm range.
I also have an NC plunger style shift interrupt switch which is in series with the coil trigger circuit, so I will test it by jumpering it out, as well.
Unfortunately it will be late Sept before we are back to the lake to do any of this......

Cheers,
Rod