what causes my truck to burn oil?

What happens when you drive local like in town or surrounding areas the motor doesn't really have enough time to probably heat up correctly that's why you don't see Either little or no smoke, or smell burnt oil. But when you drive long distances that's when the motor really heats up and starts burning oil and start to smell. A few thing are happening your piston rings are loosing there seal as well for your head gaskets. All this happens when vehicle is at it's normal temperature and the block expands. You Might wanna take it to a mechanic to verify that all your seals are working properly I hope this helps you out