Cam phasers are the biggest issue. It's a very expensive repair, pretty labor intensive and the parts aren't cheap. Typically 3-4k, the chains, tensioners, and phasers are all replaced just to eliminate the possibility of a failure down the road. The phasers allow the cam timing to be adjusted on the fly, and are actuated hydraulically with engine oil pressure. They have a locking mechanism that is supposed to lock them in place when oil pressure is lost, that is most often what fails. The result is a loud hammering noise on startup from the phaser slamming stop-to-stop until oil pressure is present.
The 6R80 is a good transmission but they are known to shudder. It'll feel like hitting the rumble strip for a split second as the converter locks and unlocks, usually under slight acceleration at mid-high speed. The fluid in them is really thin, many times a fluid change will fix it, and it should be changed pretty often, 30k miles or so.
Turbos are known to have issues here and there but it's not widespread. Coil packs and spark plugs are common failures as well, ignition needs to be tip-top in a turbocharged engine.
Performance wise they are great for towing and doing truck stuff. I have the smaller version (2.7) and it tows better than any V8 half ton I've had, the torque peak is right where it needs to be, right around 3000RPM. I get 19-20mpg average out of it.
