To flush the transmission, i pulled the return line off the radiator and put it in a gallon jug. started the truck and let it pump 2 quarts out, shut off the truck and replaced the 2 quarts and started the truck and filled the jug. Replaced the 2 quarts and put a new jug under the line and did it over and over till i pumped all the fluid out. After about 26 quarts, the fluid was bright red and i was done.
Hope this helps.
Dirk