have a 2007 GMC Yukon SLT, I haven't had one problem with this vehicle. Until I went out one morning to go to work and it wouldn't go into reverse. It sounds like its full of Steel marbles in reverse and in neutral it goes right into drive but it won't shift up when driven. But my info center says to repair traction control and stabilatrack and to services 4x4 also my 4 wheel drive **** on the dash has the 2 wheel light on and the auto light is also on and the 4 high is flashing and nothing changes when I turn the ****. I have a buddy who said he had the same problem in his 07 Silverado it turned out to be a plug was broken on his transfer case. I can't find any n plugs. Any ideas would be appreciated, thank you!