You'll just need to buy an MPVI3 device and a few credits. You might need 2 or 3 credits to unlock everything on the Tahoe. The minimum is 2 but sometimes you also have to unlock the Fuel Pump Control Module/Chassis Control Module.
The software VCM Editor is free and so is VCI Scanner. Make sure that after doing an initial read on the system in VCM Editor you make a save file such as 2012TahoeBase which is what I do.
Any subsequent alterations I make I'll write the file name as 2012Tahoe (IAT, AFR, Spark) etc so if I have to go back a step it's easier than 2012Tahoe 1 2 or 3.
Also download software called Blue Cat Transmission or BC Trans as it might be called. You can eliminate the possibility of Torque Converter Shudder and use the tables it generates to improve the shift quality and shift points in the 6L80 Transmission.