This truck was purchases pre-registered, and this was the first batch of AMSOIL run through it.
Friend runs fleet of Ford diesel commuter vans, about 100+ miles per day. He uses the 15W-40 in the older ones, 5W-30 in the newer. I believe that the quarterly oil samples showed better results with the 5w-30 in the newer engines, and also some fuel savings.
He just took one off the road with about 740K on it--engine and transmission fine, but body starting to fall off the frame, and the commuters weren't happy<g>.