Changing auto transmission oil on 72?

[storm9c1]

Is Dexron VI the new fancy synthetic stuff? Because I was told by a local shop to use the new synthetic stuff in my freshly rebuilt 4L80E (production date circa 1994, but rebuilt in 2010) on the initial fill. I already had plenty of stock of Dexron III in my garage, so I used that instead. It didn't feel right using an untried (by me) fluid in an older style trans that I just spent $$$$ to rebuild. I knew III would work, so I used it. I've also read that the synthetic stuff is great to run in any trans. Now I'm worried about what you are saying. Luckily I wasn't a guinea pig...