I have a 1999 silverado LS with the 5.3l and 190k miles. It seems to be burning a quart of oil every 1000 miles now. When I got it this wasn't happening and it just started up a few weeks back. I've just been keeping some oil in the truck and then adding it whenever the check oil light comes up. I don't notice any smoke or a burnt oil smell while driving it. There's also no leaks underneath it when it sits. What's the best way to get something like this fixed?