Just wanted to add one more succesful DIY transmission swap to the list. My 2008 Enclave has 230K miles on it and I found metal in the transmission during normal servicing. Did not want to spend much on a vehicle with this many miles so I bought a salvage yard transmission from a 2011 Traverse with 30K on it. Used my original TECHM (Valve body and TCM). Shifts smooth as ever. $450 for the transmission plus fluid and new rear main seal.
It was the original engine and transmission until now. No Waveplate or Timing chain issues. Dropped entire engine and transmission cradle out to do the swap. It was much easier than anticipated. Took two days in my driveway.