So, I have a 2004 Yukon XL Denali with a 6.0, of course. I bought it almost 4 years ago with just over 210,000 miles. It now has almost 277,000. It runs well, but I've put some money into it along the way. Took care of most the leaks, but it burns oil. I get a big puff of white/blue smoke when I...