The biggest problem with GM (and Ford) is the unions. GM also has to pay for pensions for tons of older workers. Without these requirements, I think that you would have seen GM eliminate a lot of unprofitable fluff years ago. And THEN try to rebuild market share. But they were too encumbured and couldn't afford to reduce their income.
Of course the other issue is with truely horrific vehicles. I went to the Indy 500 in 2003 and the official pace car was that SST, or as I call it El Camino's Revenge. It was booed. I repeat, the pace car was so ugly that it got booed. This was right after the invasion of Iraq and the crowd had been cheering all the different vets brought in. At this point, GM should have hit the panic button.
The other entertaining thing that GM does is every couple years they bring out this advertising slogan "We've been building crap for decades and screwing over our customers, but we've turned over a new leaf. Give us another chance." We are due for the next installment in 2006.
If GM wants to turn things around, they need to build off the one image that they have left, the muscle car. Like Ford and the new mustang, they need cars with low price, better performance, and styling that recalls the glory years. The GTO fiasco was the opposite of what they needed. Once these vehicles can find a market, use their components to build the higher margin luxery cars. If that fails, try to introduce unions to the Japanese. Because that's your only hope.
P.S.- The Tundra is a good vehicle but it isn't full sized. More like 3/4. Which isn't bad. Just not there yet. I will say that it won't be too long before Toyota starts partnering with some good American names. And then you can drive the final nail in the GM coffin.