My experience with GM diesels is with the 6.2 in a Suburban. Very poorly designed engine. Too small of an oil capacity (6qts), leading to a very short oil change interval, plus if you try and convince it to not get run over on the highway cold, it puts all the oil in the heads and starves the bearings. Also, you have to undo the injector lines to take off the valve covers. Who does that?
I currently have a Ford/IH 7.3IDI n/a swapped into my 69 F250, and it's a much better engine. Smoother, far more power, and easy to maintain. It also has a 10qt pan, so it's much easier on the oil. That Suburban was hard pressed to do 60 on the level empty, the F250 will do 70 pulling a 5,000lb trailer with room to spare.

I'd be very hesitant to try a new GM diesel product.