Just to close the issue. I put some Royal Purple Synchromax in there and it is now shifting very nice. Weather is a bit warmer, so that is helping too.
But Amsoil ATF and cold weather was not a good combo for this trans.
Royal Purple Synchromax
my trans is happy again. Wallet is lighter though. 18 bones a qt. must have some gold dust in it.
Strange though, I can't tell you how many other MN6 cars I've put Amsoil ATF in and they all shifted great. Maybe it's like when Coke screwed with the formula. New Coke sucked. I had the same feeling pouring 40 bucks worth of new Amsoil down the recycle tank at Autozone.