They run very well, but get your money out. On the pickups, just like with Ford, GM forces you into a higher trim level and giant cabs/tiny beds, so the MSRP is well into the nose bleed section. Granted, the Suburban will only have the one body, and there is no base trim anymore in them, so you'll already be in small house territory for cost. I would not be surprised if the 3.0L diesel version is in the $70k neighborhood. The Sierra I test drove with that engine was $63k. For a half ton pickup that has a tiny bed.
I know people get all wound up about the Gilmer belt running things at the rear of the engine, which eventually will need replacement and requires transmission R&R, but as someone who works in the industry, I can tell you that there is a pretty high chance the transmission itself will need replacement by that time anyway. GM still hasn't mastered slushboxes, despite making them longer than anyone else. At least they are not terribly hard to swap out. Even the 4x4s are fairly straightforward.