Pete,
Forget everything, THIS IS ABOUT YOU.
Selling cars is a team sport. You need to see a strong commitment that your leadership wants change and is ready to back you. Without it, you will fail and waste 1-2 years of your life.
DANGER DANGER DANGER!
The worst HIPPOs ever are Fat and happy mulit-millionaire Dealer Principals (F&H DPs). "Business Improvement" to these fat and happy HIPPOs totally not your definition of "Business Improvement". When you discuss "Business Improvement" to F&H DPs, an awesome idea is to them is change nothing and get more money for it. They are 1000% ready to overlook all of the lost opportunities just as long as they see no threat to their giant pipeline of incoming cash... Sorry Pete... the F&H DP sees your ideas as a cost -with- potential risk to his pipeline.
Remember, leadership buy-in is NOT your responsibility. THEY should be the agent of change, YOU should be the tool to help implement their plan. With a half-assed leadership buy-in, WHEN you make one mistake, the rank and file (that has been fighting you all the way) will "throw the rope over the tree" and double down on their resistance to your plan.