GM is a fat mess. The management team which were replaced after the bankruptcy are all people that were managers when the last managers ran the company into the ground. GMs has several issues that FCA and Ford do not have.
One, GM wanted brands like Chevrolet to have a vehicle in every segment. It didn't matter if the company was hard up for development money or what. But if Chevrolet could have a potential car in every segment, GM would sell a car. Didn't matter how much it cost to develop, GM's bottom line was sales numbers. Even if the segment was a dud, sell sell sell.
Second, brands that have vehicles that compete with one another. Chevrolet just introduced the all-new Chevrolet Blazer CUV which will compete against the Ford Escape and Jeep Cherokee. It will also compete against the Chevrolet Equinox. Makes sense? Then you have Buick competiting with premium Chevrolets and GMCs. The brands all compete against each other. Alan Mulally, come up with the "One Ford" method. Build one Ford globally for a segment. The Lincoln brand has now pushed their brand to the point that it doesn't compete with Ford. Sergio Marchionne made FCA have one car per segment. Thats why you see a three-row Durango and a two-row Grand Cherokee (but no three row yet). It sounded stupid, but it worked.
Third, manufacturing plants. GM has a knack for having more plants than it can deal with. Instead of having flexible plants that can run multiple architectures (example, FCA Windsor builds both RT and RS minivans and Toluca builds the 500, Compass and Journey), their plants run like one or two shifts instead of being at full capacity. Sergio never wanted to build a new plant. Instead run all the current plants at full capacity to ensure jobs were kept and lower cost of operation overall. GM can't figure this out. Instead, now GM is keeping the last generation trucks for example. They are partially assembling them in Fort Wayne, Indiana and then shipping them to Ontario to complete the assembly process.
GM is out of control. Trump is upset, because he helped cut regulations for the big-three where Toyota, Honda and Nissan didn't want the cuts because they sell passenger cars and GM builds products that are passenger cars here in the U.S. and half of their truck line is built in Mexico and Canada.