Commenting on an old thread but I used this GM fluid:
ACDelco-10-4006-Synchromesh from Amazon and it made a newly immediate difference in shift quality and cure my third gear clash I was experiencing.
I changed the factory fill at 120,000 miles and ran G072 (I think) until about 160,000. I had problems with third gear for the past year until I used the GM Syncromesh.