GM could save themselves a lot of money simply by eliminating GMC. Everything GMC markets is duplicated by Chevrolet. Now, decades ago GMC actually mattered as the "truck division" of GM, but that hasn't been the case for a very long time as the products are mirrored across its sister company.
I still believe a big mistake was eliminating the mid-size SUV platform and trying to migrate their customers to an inferior crossover. That cost them market share to Ford and Jeep, to say nothing of the foreign automakers.