This is an old thread, but we had a bus stop in our shop yeaterday with this same problem in a b500 transmission, '94 vintage.
Our tech simply removed the Allison transmission shift contol module and carefully opened the box to expose the circuit board and pushbutton pad.
Using a Qtip dipped in either, simply clean both the board contacts and the magnetic points in the keypad side.
Reassemble carefully and plug back in, works like new. A new module lists for 2900.00, so if you experience this, don't be too hasty in purchasing new.
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