Also, if that much oil were vaporizing the crankcase breather hose that leads to the intake manifold would be wet with condensed oil vapors.
It is possible for carbon to build up on the piston ring lands and casue them to stick and not make a good seal with the cylinder wall allowing oil to get into the combustion chamber, as well as combustion gasses to blow by the rings and contaminate the oil. Sometimes, using an "engine flush" where a cleaner is added to the oil right before an oil change and the engine is allowed to idle at operating temperature for a few minutes before draining the oil sometimes does the trick.
I have used Mobil1 oil in the past on a F-150 I used to own that I drove an average of 600 miles per week, and afer a few months of using Mobil1 I noticed an increase in oil consumption. I used an engine flush, then switched to Castrol Syntec and after 2 oil changes while using castrol and engine flush before draining the oil the problem went away.
