I can think of two possibilities, neither of which is technically Bonneville-specific:
1) The Torque Convertor Clutch solenoid is stuck on, which basically locks the engine to the drivetrain, as if you were in high gear at highway speed. Not sure if this should affect Reverse as well, but a malfunction is a malfunction.
2) You've got a massive vacuum leak, which is doing Gawd-knows-what to the ECM inputs; the computer may be getting no usable signals coming in and is operating in some kind of puke mode. Sorry about all the scientific terminogy there.
When the engine is running (when you're in Park), do your ventilation controls work properly? If you dial up the Vent setting, can you get air to blow from the dashboard vents, or does it blow through only the floor vents or the defroster vents, no matter what setting you select? If you can't get Vent mode to work properly, you've got no vacuum in the system, and you'll want to check under the hood for busted or disconnected vacuum lines. Start with the black, round sperical booster reservoir on the firewall near the passenger'* side wheel well, and follow the lines from there.
That'* all I got... I'm guessing here, but see what you find out...