Bodon, I would recommend using an AMSOIL product. Below is the recommended type of transmission fluid. You would need 12 quarts for a transmission fluid change. Shoot me a note if you have any questions.
Same as I used when the Circle D converter was installed in my 2014 GT auto. 6R80 with Circle D FTW!!! It's a total 12 quart fill with the transmission cooler 100% empty. However, you will only need 10 quarts because the transmission cooler will not lose hardly any fluid when the transmission is removed. I put 9 quarts in mine, and was almost full. I may have got .5 more quarts in it to top it off.
That link is a direct quote for a retail 10 quart (2.5 gallon) jug, exactly what I bought for the job. Preferred Customers only pay $86.00 + shipping & tax. You can see the difference in size of 1 gallon vs. 2.5
You will want this pump to do the job. It has all the proper tube lengths for Amsoil quarts and gallon jugs.
I should have sent in the lubricant for testing from the transmission I destroyed. Pretty confident it would have come back as usable. However, it was littered with clutch pack material and metal shavings. The overdrive clutch could not handle twins. After the clutch pack failed, it put excessive strain on the intermediate shaft.
Overall, it's a tough product, normally lasting twice as long as your average formulation. The natural lower frictional coefficient of the base oil will also help decrease transmission temperatures. No matter how hard I run this car, I can't get transmission temps over mid 190's.