welcome to JA, i will try to help. the only two things that come to mind is either a PCV valve bad which is the least expensive or an internal engine problem(piston rings bad). if you have no issues with driveability i would try the PCV valve.
the test for cylinder leakdown and compression will determine if it is in the head or the piston rings.
ASE Certified Technician
worked at a GMC,Cadillac,Pontiac dealer, GM trained in all models