Flashing OD indicates an internal fault and or overheated fluid. A flashing OD after long highway drives is a sure sign of slipping and overheated fluid. Park it until you can scan for codes. If you continue to drive it, you will need a rebuild. You can check the fluid level in case they over or under filled it. The top mark is the cold fill and the bottom is the hot fill. The engine has to be at idle for a measurement. They also may have used the wrong fluid.
jeff
