new user here. Went straight to my two oldest trucks. "A" is a 2004 Savana 3500 6.0 gas which is a bit of a factory freak. Over 400k miles and still runs very well, no oil consumption. Truck "B" is an 07 same make and model. Both work daily, 5-6 days a week. Curb weight is 9200 pounds. "A" has a bit of lifter tap and piston slap when cold since new, "B" has a driveway rebuild with everything new from the cam up at 250k miles. Uses some oil, no smoke or noise.
As an example of how hard we work these trucks, "B" used over 400 dollars worth of 87 last week!!!
Added 16 0z. Kreen to each today with 10w-40 Castrol GTX (on sale) and a Pure One. One truck went out to work (B) and one stayed home to run here (A) - stationary operations at about 1500 to 1700 rpm for 2 or 3 hours.
I don't expect a big change in A. It runs too good already. But B uses a bit of oil, sometimes a quart in a week. We thoroughly checked it out before we rebuilt it, the bottom end is quite sound. I'm thinking it may have sticky coked up rings.
Cross your fingers for me!