vehicle speed sensor- cat C7-allison trans combo

Got a funmover 39c on an f750 cat c7 chassis with a speedometer going wacko....one second at 0, then 90, bouncing around. Would be easier to service if the engine wasn't cutting out thinking its over speeding when the needle bounces to 90-100 mph . Worried it may die before I can get it to a shop. Would like to fix at home. I understand the sensor ties into the Allison somewhere, but where? Do they just come loose as well?

For frame of reference my truck is front engine.


Thanks,

Cb