I didn't sample the oil in this unit until 47k mi. Results posted here. Fe and Al levels are high and could be cause for concern, but I'm going to watch them during subsequent intervals. Engine is unmodified and no use of oil additives, only fuel conditioner about every other tank. I'm inclined to go to a 5/40 oil but the truck has another 50k worth of extended warranty, and we all know how quickly a non-dexos2 oil would be used to void a warranty claim in the event of catastrophic failure (hole in piston etc), despite the oil type not being of relevance to the failure mode.