Getting codes for Vehicle Output Speed Sensor and stuck in 1st gear.

• Check the resistance on the speed sensor mounted to the Allison transmission. 
• It should be getting roughly 2.3k-2.9k ohms at 77 degrees Fahrenheit outside for the 2009-2015 models.
• Another way to test it is by checking the voltage on the pins. Make sure the vehicle is in park position with the parking brake engaged, and slowly rev up the engine while observing the voltage increase with a multimeter.
  The voltage should increase smoothly with no dropouts or glitches. The voltage amount can vary from 0.15 volts @ idle all the way up to 15 volts at higher engine revs.

Here is a video that may help.