Duramax Diesel P0101-C Still working on it

Ok I got the P0380-B glow plug code fixed there were 2 bad glow plugs. Now I did find a hose clamp lose. And thank you for the tip on reading the articles on P0101-C. Remeber I already changed the MAF sensor. I found a possible cause paragraph / things that could set a P0101-C code in my scan tool that stats, (5 Volts Reference Circuit, Air Filter Element, Barometric Pressure Circuit, Boost Pressure Sensor, Charge Air Cooler, Diaphragm, Engine Control Module, Exhaust Gas Recirculation, Throttle Valve Solenoid, Exhaust Gas Recirculation Valve Solenoid Valve Diaphragm, Exhaust Gas Recirculation Vent Solenoid,
Exhaust System, Hoses, Ignition 1 Volt Circuit, Intake Air Temperature Sensor, Low Reference Circuit, Mass Air Flow Sensor, Mass Air Flow Signal Circuit, O-Rings Seal,
Secondary Air Injection Induction System, Turbocharger, Unmetered Air,
Wiring Harness / Connectors) What dose the B or C after the code mean? I did put a new air filter in that was the frist thing I did. That is a lot of things that can set the MAF code where would I start? Please help Beam

So the owner of the truck says that the truck has had this MAF sensor code P0101 like from the frist day they took it off the lot branb new. I not sure I beleive that is really true. the truck has 108 K on the truck now. I am suprized I didn't get any replies on this topic yet. I really need some help with this code. Dose anyone have any ideas where I should looking or what I should do next. Beam

Check power and grounds. Inspect the connector for damage, pins pushed out, etc.