@deerslayer1985 : Sounds like there's a fairly good chance it would work ... since they are only 1 Model Year apart ... and they have the same Engine. I know ... with my 2011 Equinox (3.0L V6), it has the "6T70" transmission ... but if I had bought the 2.4L Engine in the same Model Year, it came with the "6T45" transmission ... and so ... they're definitely
not interchangeable.
I guess I would start by looking at VIN numbers? I believe there's a digit in there that designates the Transmission. Then, check the RPO Codes on both vehicles ... to see if they have the same Transmission Code? Then, look inside the Engine Compartment for a tag affixed to the Transmission Housing ... and see if those numbers match. You could also stop by the Dealership Parts Desk and ask the person there to look it up for you.
But even if the two Transmissions physically bolt-up, the other question would be ... are the Electronics interchangeable? Would you be able to bolt your Transmission Computer onto the G6 Transmission? That's another question for the Dealer Parts person.
Hopefully, though ... your Fluid replacement will allow you to avoid all this aggravation. I once avoided a Transmission Rebuild/Replacement on my 1997 Taurus Wagon simply by changing the way I drove the vehicle: No sudden takeoffs from stops ... just light, smooth acceleration. This avoided the slipping and "hammering" going from Gear 1 to 2 that would've eventually destroyed some hard part inside (Forward Clutch/Piston?). Drove all the way to 230,000 miles with no major repair bills!
Good Luck!