Buying 2011-2012 Impala

Hi, I'm looking at purchasing a 2011 or 2012 Impala, I noticed the 2011's were the last model year to have the 3.5, 4speed automatic and the 2012's have the 3.6 6speed automatics. Would either model be reliable? I've noticed from reading postings about speeds can be reduced to 15 miles an hour due to the traction control and engine light coming on which sort of worries if that were to happen. Is this a problem that happens on all Impalas when they reach a certain mileage? Any input would be helpful. Thanks in advance.