I had a '99 2500 Silverado with a 6.0L and it used a little over a quart of oil every 3,000 miles or so since the day it was new. The dealer told me that was acceptable. When I traded it in on my '14 1500 Silverado with a 5.3L it had 176,000 miles on it and burned exactly the same amount of oil as new. My '14 has 21,000 miles on it and it doesn't burn any oil at all.