I had not experienced a smoke or oil problem until last month.
I left Edmonton, Alberta, driving to Pennsylvania, Philadelphia. The drive there was uneventful but on the return trip, I was about to leave Ohio on I-80 when the 'Check Engine Oil Level' indicator turned on. I pulled into the nearest truckstop, found the location of a GM dealership in Bryon, OH and told them of my situation. They took the truck in for a brief check and indicated to me that everything was alright but that the truck was experiencing a sensor malfunction and that I should have it replaced when I returned home. Satisfied, I continued my drive home until I arrived in Chicago. Using OnStar, I located another dealership, which they guided me to, turn by turn. Upon my arrival, they examined the truck quickly and repeated what the other dealership stated, that it was a sensor malfunction. They offered to book me in for next week Wednesday, but I declined. (It was Tuesday, and my sister's wedding was the coming Saturday.) I continued for several more hours, then stopped and decided to check the oil myself. (Something I should have done in the first place, but I thought I would take advantage of my warranty situation.) Imagine my surprise when I found the oil level was so low that it didn't even register on the dipstick! I was at a Mobil station and purchased one quart of oil and added it. This brought the oil up to where it barely registered on the dipstick, so I purchased another quart and added it, bringing it to the safe level.
Upon my return home, I immediately had my oil changed. The 'Change Engine Oil' indicator had not come on yet, but I feel the oil was probably burned quite badly. My dealership took it in next week and replaced the PCV valve as well as the valve cover gasket, very similar to what chevacc indicated. The shop foreman told me that an engine has to burn two quarts every 3,000 miles before GM considers it an oil consumption problem, but they took mine in anyway and found the problem with the PCV valve.
In addition, I am preparing a letter to produce to GM and my dealership, outlining the issue I had with the dealerships in Ohio and Illinois. Hopefully, something positive can come from this. At least the engine is operating fine, with no issues.
Just my two cents.
P.S. The engine no longer burns oil. (That was the first and only time.)