Don't forget that GM ran plants to make products that were sold at no premium or even a loss, as the jobs bank agreement with the UAW resulted in no savings if the plant were idle.
I had seen some breakdowns of which product lines were profitable, and if anyone asks why big trucks were popular in the 90s up until that bubble burst, does not understand that the trucks kept the whole company above water, by a little. It was clear once gas hit $4/gallon in 2008, and truck sales hit the skids, the crap was hitting the rotating airscew.
There are many other things that you know from being on the inside. It was often amazing that any of the automakers were making a profit.
There have been many books written on the automakers. I am not sure it has all been captured in a clear way.
I will read those papers.