General Motors plans to offer two separate versions of the big Chevrolet Impala, both the 2014 remake of the full-size sedan as well as the old model that it was intended to replace. The previous-generation Chevrolet Impala will remain in production indefinitely and will be aimed strictly at the fleet market while the all-new 2014 will focused on the retail market where Chevy hopes to pick up market share, GM officials said.