Blow-by

Has anyone pulled the oil fill cap on their truck and noticed blow by? I realize that some is normal in a diesel, but mine seems to puff smoke pretty consistently. I didn't check for blow by until my truck threw a P0172 code which reset itself. According to GM service info diag the code can be set for bad fuel, fuel injector flow, or piston ring issues. I am probably going to take mine into service and have it checked out I am just wondering if anyone else has noticed it in their trucks. My truck has almost 14,000 miles on it so break-in shouldn't be an issue. The truck also doesn't appear to be using oil.