My experience is only with the 3060 tranny and W-TEC II control. On the version I have, the TCM shuts off the exhaust brake at 10mph and below. Depending on the control you have - you should see the target gear change back to 6 (or highest) when you get to 10 mph and no foot on fuel pedal.
On mine when cruising above 10mph and I take my foot off the fuel pedal, the tranny switches it's target gear to 2nd and depending on the RPM, will start downshifting toward that goal - at 10 mph it switches back to 6th gear (that's when the TCM shuts off the exhaust brake).
That being said, my brake is not being turned off either - the signal that is supposed to be on pin 132 of the TCM apparently is not there. I am adding a foot switch so I can disengage the exhaust brake when under 10mph - not an ideal fix but easy enough to implement. I ran the wires yesterday, just waiting for it to arrive.
I may send the TCM in to this company for repair - have to call and talk to them first
ECM King - Allison Transmission ECM