If the level looked near max on an incline as long as it wasn't a stupid gradient then it can't be that far off if you were on level ground. Best thing to do would be to get the code read as there obviously has been one thrown up. If visibly the coolant is not boiling, nor are the hoses pressurized or the engine smelling hot then I wouldn't take what it is saying as gospel just yet. I take it the temperature gauge wasn't in the red zone or you never looked at it? I take it these models do have one.