Wait, what exactly did you run? Dex III, Dex VI, or Mercron?

Dexron is a GM spec fluid. The old spec is Dexron III. This was replaced a few years ago with Dexron VI. All GM transmissions old and new can run Dexron VI fluid. And they should as that fluid is much better than Dexron III.

Mercron spec fluid is not a GM approved fluid and is not recommended in GM transmissions.