I just bought a 2016 Sierra 2500 HD gasser last Friday. We had a snow storm on Wednesday and I used the 4WD for the first time(manual floor shifter). There seemed to be laboring on the engine while in 4wd drive. The RPMs ran about 2500 higher at 45 MPH also. Took to the dealer and they have no idea what is wrong with it. They are going to start taking the front differential apart today. I don't like the idea of having them replace parts instead of replacing the whole diff. I did not buy a new truck to get a rebuilt front dif right away. Any other 2500HD owners have this issue? Anyone know how to get GM to replace the whole differential or whatever other part they may find as the cause?