Just recently did this on my 2011 LT Tahoe @ 75,000miles. (see my post here) Additional info to that above:-
1. Removing the little clip that secures the line into the radiator required a little pick
2. If you dont use a fitting, the 3/8" OD plastic tube will pop out of the radiator. I just held it there while my accomplice ran the engine
3. The cross pipe below the transmission pan prevents the pan being pulled forward. I used a clamp to pull the exhaust down as far as it would go to give clearance to remove the pan.
4. I struggled getting the securing clip properly reinstalled. I think the better way would be to replace the spring clip first, then insert the transmission line, then reinstall the plastic retaining ring.
I used a total of 14qts Dexron VI for the flush/fill process.