PickupTrucks.com adds that GM has its own excellent team of diesel engine specialists that are fully capable of designing the automaker's next heavy duty truck engines. In fact, the 4.5-liter diesel that had been planned for light duty applications was wholly engineered by GM. Okay, got it.
But wait. According to Green Car Advisor (sadly without citing sources), Isuzu has proposed that it develop a new HD diesel engine for GM. Both reports could be true; Isuzu may have decided that it should continue to work with GM, and that could have led to the proposal, but we can't say for sure.
GCA also indicates (again, without citing a source) that GM and Isuzu are also in talks that would have the Japanese company take the lead in developing new pickup trucks for Southeast Asia and South America. GM's current Chevy Colorado and GMC Canyon pickups share common underpinnings with trucks that Isuzu developed for overseas sales.
[Source: Bloomberg, PickupTrucks.com, Green Car Advisor]