The major problem GM had 20 years ago and still suffers from now, is viewing all engineering decisions through an accountant's cost trimming eyes.
Lets take two common examples, although certainly there are countless others from the last 25 years.
1. Olds 350 diesel. (1978 - 1985)
2. 3800 Series II V6. (1995-2005)
GM failed to understand that compression in a diesel is such that headbolts/head gaskets must be of prime importance in designing the powerplant.
However, it took GM 5 years of consumer problems and class action lawsuits to finally come up with a headbolt design coupled with a gasket that effectively halted the problem.
But..after 5 years of denials, and repairs done with parts that were identical to parts that failed first time around, GM and the engine's reputaion was damaged beyond repair for many customers.
The original 350 diesel block, code named the "D" block had weak casting and was subject to cracking.
Time to GM's addressing this issue..3 years. The engines debuted in 1978 and this block issue remained until 1981 with the introduction of the 350 "DX" block on all cars with the 350N.
Who remembers the under engineered TH200-200C-200r4 trannys ? At the time, I worked in a used car dealership. We often swapped out a 200 series transmission for a TH350C which often bolted up..and was infinitely more durable.
About the beloved Series II, prior to the engine's update in 1995, UIM failures were scarce for the older Series I 3800.
But with the upgrade in power, the engine saw it's UIM swapped to a plastic composite material which had a very hot EGR chimmney running between cooling ports to the throttle body.
In short order, reports of warping, external and ruinous internal coolant leaks started popping up.
After denial, a redesign of the OEM composite and a little later, a slight redesign of the LIM occurred about 1999.
However, the failures continued.
About 2000-2001, GM did a recall which consisited of new bolts for the UIM and coolant tabs. But as anyone that has seen these UIM's EGR tube "rot" out due to heat will tell you, coolant tabs would have little affect.
Finally, after much owner suffering, in 2004 GM updated the 3800 Series II into the Series III which now had electronic "drive-by-wire" throttle body, and a not publicly mentioned "aluminum" UIM which now effectively stopped the EGR heat in its tracks.
Time to repair the issue.. almost a decade.
I have retro fitted a 2004 aluminum UIM onto my Series II 3800. All I can say is why does it take GM years and countless customers to fianlly fix things? Also, why do they continue to design things like the composite UIM in the first place?
This was not a high tech fix...yet it took a decade.