i would get ready to take the chevy dealer to small claims court-- they sold you a car with an issue, "misdiagnosed" it till it was out of their warranty period. they should be covering it 100% since you brought it to their attention during their warranty period.
Past: 2001 330i ZSP/ZPP/Step
Past: 2004 S60R 6MT Sport
Past: 2007 335i 6MT ZSP/ZCW/322/655
Past: 2010 335xi ZMP/ZCW/ZPP/PPK/PE
Present: 2013 335i 6MT ZMM/ZDH/ZTP/3AG/494/508
Current Homeland Threat Level: