Hi, everyone. I searched for this issue and wasn't able to find anything with the symptoms that my truck has so I decided to start a thread.

2012 2500HD, 6.0L, 6L80E, 210,000K, Original trans. w/ no prior issues. Fluid level and quality OK. Periodic maintenance always performed on time. Truck has never been "worked" and 90% highway miles. Transmission now shifting at very high RPM (resembles when tow mode is engaged) and will not shift into overdrive at all. Shifts are smooth both up and down, no vibration. Makes a whirring noise at engine start and when standing still in D, quickly dissipates once moving again. Check engine light has come on. This happened 500+ miles from home in that snowstorm on Thursday. Reduced speed to 50 mph and made it home in one piece.

Ring a bell with anyone? Suggestions? Thanks!