2012 Mazda 3 2.5L Auto trans problem
 

I have a 2012 Mazda 3 2.5L with an automatic trans. When i come to a traffic light, the A/T comes on for about 2 seconds and then shuts off. Then when attempting to get moving again, the jumps as if it were in neutral and dropped into drive under acceleration. I have been doing lots of reading and from what i can see, short of a new trans, it could be a speed sensor or a simple fluid change.
The problem i am having is this, when i try to get a sensor, i am being asked if it is the input or output sensor. When i look at the mazda parts list, they only show one transmission speed sensor.
I am also trying to figure out where it is (or they are) located?
Any help is much appreciated.

Take it to Mazda for a diagnostic scan.