Not to add to your workload, but if $20k or whatever is a decent chunk of change and worth some more emails and calls, I wouldn't take GM's canned response about dealers being independent, blah, blah, blah. This is the first time that GM has done a reservation style deal (to my knowledge) and how were you to know your selected dealer would try to shaft you after you ordered the car, etc.
I think squeaky wheel can get the grease. Call and email GM customer service and any other relevant department at GM over and over again and explain the collusion and how you were misled by your long-time dealer, etc. Cause problems for the dealership and you might get your car at MSRP.