Small things are, in their own right, quite capable of bringing down giants with not so much as a small action but at a cumulative level. With the little defects affecting GM products accumulating to a record braking level in 2014, it is a surprise that the company is still in business.
The Chevrolet Impala has racked up quite a rap sheet when it comes to defects and other niggles that bugs the car. You may want to hold onto it maybe because it emerged onto the car market at the turn of the millennium. Chief among the reasons as why you should sell is the high number of complaints (124) logged with the NHTSA voicing concern due to the engine.
Other problems are in the interior accessories and the transmission. It would make no sense keeping this in your garage as its market value dwindles further.