On the data tag in the driver's door opening there is a TR. Under that is a letter. As I remember B means 4R75E, which is what I believe is in your truck.
I don't remember the complete fill for that, I think it should take about 15-16 quarts to do the flush.
You'll also find that the cooler lines are one above the other, not front and rear. Someone should be along shortly that knows which one is in and which one is out. I don't know.
Use MERCON V, do NOT use MERCON. I'm not a fan of Amsoil. I like Mobil 1 synthetic ATF. Any fluid that is MERCON V rated will be fine.