Did i just totally screw up? I drained the tranny when I replaced the shift solenoids and didn't even notice it was dexron vi until after I put it in...

If you've not run the car since you should be able to drain it and put in T-IV without problems.

I thought the 6G took Dexron3, not T4.

Hmm, if it takes DEX-III then the DEX-VI would be ok. Tried finding information but all I could find with a quick search were fluids based on the car, and all the fluids suggested by Amsoil and others meet DEX-III spec and not T-IV. An owner's manual would have definitive information.

D2 is spec'd, but obsolete, use D3 or D3 compatible fluid, D6 is supposed to be backward compatible but is a bit thinner, is probably OK, may shift a littler harder with thinner fluid...maybe? Shouldn't harm anything inside. I like Valvoline Maxlife ATF, pretty much goes in anything, synthetic, good additive package, has some seal conditioners.

https://en.wikipedia.org/wiki/DEXRON
Ok, not as much of a difference, actually more stable across operating temps, should be fine!