GM themselves have very few innovations to their credit, although two big ones, the Hydromatic transmission and the Comfortron fully automatic HVAC are fully theirs.
Many of the inventions appeared before GM was formed, or before the marque became a GM product; or in later years, others invented it; be it another automaker, or a supplier to the automotive industry. Often times, its the supplier who invents the idea first, an example being Perfect Circle with their Speedostat who have to 'sell' it the auto industry to see if there any takers. Chrysler was the first to make it a regular production option. In Packard's case, it was Dana who came out with the limited slip differential, and Packard was the first to use it in 1956 and Studebaker in 1957. It was the same situation in Europe in a lot of cases, where it was Triplex Glass in England who invented the common rear defogger we see today on most cars with the thin metal trips that appear as wire on it (Triplex called it 'Hotline'), and sold the idea to British automakers who immediately picked up on it.
Craig