Tow it to the dealer. Only GM ties up all their software downloads to prevent independent shops from working on their cars and saving you money. It's that type of business practice that separates owners from their money after the sale and keeps GM profitable. If you want a customer-friendly company you'll have to go with a Chrysler, Toyota, or Hyundai. All of Hyundai's downloads and access to the web site are free.
You also want the dealer involved in repairing this ridiculous system. That will make them part of future lawsuits. This is the same throttle-by-wire system that made news for Toyota. I shudder when I think about all those cars coming at me on the highway.