Just changed the lube in my 4500 with 2qts MT-90 and 2 qts MTL per Dave @ Redlineoil and oh my goodness what an improvemnet in shifting! It literally falls into the next gear nearly effortlessly. Truck has 121500 miles, bought it used so don't know if it has been changed and what fluid was in it. Anyway great improvement and wanted to pass it on.
Anthony in Idaho
Anthony in Idaho