There seems to be a lot of posts on the ASRC vs Mobil 3309 transmission fluid. I just changed the fluid in my 15' 3500 with the Mobil 3309. Based on the manufacture fluids sales brochure it seems the critical item is meeting Type T-IV, which as you can see in the attached pictures Mobil 3309 meets. Hopefully this posts helps someone who is on the fence about which fluid to use, in this economy saving money anywhere you can helps.