Well I am getting my car back tomorrow morning without a satisfactory answer. The dealer admitted that mine was not the only Dinan Stage 2 550xi in for a drivetrain malfunction warning but rather there was another car in as well.
The dealer says that, according to the computer log, the drivetrain malfunction warning was triggered by a low fuel sensor which was triggered by a low fuel condition. That is complete bull**** because I never allow my gas guzzling car to go below a half tank because it's range is so short. And when the warning came on, my fuel level was at least one half.
Therefore, I have received no valid explanation for why the malfunction came on and why power was reduced. Hopefully the problem will not recur.
2012 Dinan Stage 2 550i xDrive M Sport, Imperial Blue Metallic, Cinnamon Brown Leather and Light Wood Trim. Major options are M Sport package, cold weather package, sport automatic transmission, active roll stabilization, premium sound, and side and top view cameras.
Dearly departed BMWs: 2009 550i M Sport in Carbon Black Metallic and 2003 540i M Sport in Titanium Silver