Re: allison transmision not shifting from stop
You need to know if the transmission control system is getting its throttle signal from a throttle position sensor dedicated to the transmission, or via engine to transmission communication.
If it's got a TPS for the transmission, the linkage might be sticking making the transmission ECU think you're on the throttle. This is a pretty common malfunction on vehicles of this vintage.
It may have some other input sticking. For example, some vehicles have a brake pressure switch wired into the system so you have to be on the brakes, closing the switch, before the ECU will allow a direction change.
There' also a very slight possibility the transmission sump thermistor could be reading extremely cold, preventing range from engaging. I've also seen false output speed readings cause this kind of complaint. There's also a slight possibility the turbine speed sensor could be faulty, making the ECU think the engine is turning faster than it really is.
Just a few ideas to get you started. The best way to check it of course, is to plug in a Pro-Link or Allison DOC to see what the ECU is thinking. That usually leads to the root cause pretty quickly, assuming the operator of the tool knows what he/she is doing.