I purchased my TCCM from GM Parts Direct. It cost about $200 Shipped.
Here is how you replace it.
First take off the panel under the steering wheel and the pannel that is below that
This is what you will see from under neath the blue clip goes into the TCCM there are 3 different plugs that clip in there. It is right behind the metal plate that you will see when you take off the pannel, It is all the way to the drivers side.
These are the 3 plugs after you take them out of the TCCM They unclip pretty easily but require a little contortion to get your hand up there to them. I am sure you could just take more stuff off but this wasnt too bad.
This is how they go in the TCCM. Note, you cannot put them in before you pop the new TCCM into its bracket. This is just so you can see the order of the plugs because you won't be able to read the label on the TCCM when you put it into place.
Clip the TCCM into its bracket, and install the plugs. The small black plug goes all the way to the passenger side, I labeled them in the drawing.
Put the dash back together, go to the dealer and get it programed.
any questions just ask here, don't PM me