I am confused and don't flame me if I am wrong.

So if the D-MAXX and the Colorado were joint ventures (doesn't matter if Isuzu did most of the work on it), then how is Isuzu making a clean new start making the Trooper on the D-Maxx chasis? How is that a totally new design from scratch without GM involvment?

This isn't to start a war, it is just a question on technicalities.