Transmission Upgrade/change

[hsaddock]

Folks:
I am giving serious thought to changing the transmission in my
83FC35 from the Allison MT641 to an Allison MD3000. The reasons
are: 1) current transmission with 112K miles on it shifts a little
slowly from 1st to 2nd at full throttle - it shifts just fine if I
back off the throttle slightly and in all other gears. (perhaps this
is the beginning of a bigger future problem?) 2) I want to travel a
little faster at top-end, and the MD3000's 5/6 speeds gives the
overdrive(s). 3) I want to pull a little better going up steep
hills so if I lower the differential ratio while doing this
conversion, I can pull better in the lower gears and still tool down
the road faster on the flats with the overdrives.

Has anyone tried this conversion? Comments on anticipated issues?
The MD3000 appears to be an inch shorter in length than the MT641
and a similar bolt up pattern so I don't expect to see any major
issues with mounting. The MD3000 is computer controlled - can it be
fooled into working with an older 3208?

Harry Saddock
83FC35
South Windsor, CT