Reverse Lights

[owemon]

I had my Transmission rebuilt in February and when it returned from the Garage, my reverse lights were out. I took it back and they told me it was a module on the transmission that needed to be replaced. Does anyone know what part this is called? How difficult is it to repair? I have a 2000 Chev Tahoe. Thanks for your help

 

["EO" hat]

Don't let em push it on u, the lights functioned before the rebuild right?