If you go to the TRAXXAS site and download the user's manual for the T-Maxx and look on page 38 you will find a good explanation about the tranny and its screws. It will also explain how to adjust the tranny shift screws.
My advice be very patient. I got so frusterated I almost bought a new tranny.. Yeah $80 worth of frusterated. Small 1/8th turns man. Sooner or later it will shift. Ohh shoot...
If somone loosened the set screw instead of the shift screw, it again won't shift. Try adjustting if that don't work have a peek inside.
I just got off the phone with TRAXXAS, and YES, they do have different settings on each Maxx they make. The grub screw is installed by the computerized robots and there is no magic number. The 6.5 might have come from someone dismantling it on their own and figuring it out.
When asked what a good starting point is, the tech said with the tranny open and the gear set in hand put the shift set screw so that the top of the grub screw is just flush with the top threads of its threaded recess. From there use 1/8 turns in or out until the tranny shifts as it should. He also recommended using a spot of medium loctite on the set screw to minimize any vibration caused backing out of the set screw. From there, I refer you back to my original post for obtaining the procedure for making the adjustments.