OK .... how s it that this guy has OD lockout on his 02 and I don't? Or do I and just not know it? How is it engaged?

http://www.dieselplace.com/forum/showthread.php?t=292461&highlight=Overdrive+lockout

It was a retrofit. Due to customer demand, Allison provided a service calibration through GM that would enable it in the TCM. Then the owner or dealer had to wire it up.