[Stephen12ZL1]

the tranny is definitely overfilled and hopefully has the correct fluid in it. The techs are lazy and get it "close enough" and don't get the temps high enough to bleed off the correct amount. You can do it at the track but you have to be careful and wear gloves...the hot fluid is no joke so be careful. I personally have adjusted standard ZL1 fluid levels on 3 different cars at the VIR garage. Two of them the fluid level wasn't correct from the factory which isn't surprising...overfilled.

Manual vs auto shifting (no matter what GM says) is simple...more shifts equals higher transmission temps and less shifts is cooler. At VIR "A" mode shifts and downshifts many more times than paddle shifting making temps soar. I also have an opinion about 15w50 causing the oil temps to be higher from parasitic drag of the oil pump. Stirring that molasses is tough for the oil pump and makes oil temps 20° warmer in my experience. I use Motul 5w40 competition and it has worked great.

For tranny fluid I have been using Amsoil fluid (signature series fuel efficient) which is appropriate/approved for the 10spd with success. It comes in squeeze bags and makes it a breeze to place the fluid through the necessary port.

Hopefully some of this helps and I wish you success getting your temps down!