I have a 2013. Absolutely awesome truck. Zero issues, I have got two tsb's for an abs reflash and a trans reflash. Tow regularly with it. It handles my car trailer, enclosed, like it's not there and the exhaust brake is wonderful.

2013 was the first year of def in the 2500/3500 trucks, but it was used in cab/chassis trucks for several years before. I have not heard of many problems with the systems. The biggest gripe is the def tank uses a sonar type sensor so the gauge isn't linear like typical fuel, but def freezes so you can't you a float setup.

I have never plugged my truck in in my 2 years of ownership. It hasn't been above 10deg here for two weeks nearly and not one issue.

You barely notice regens. I can't recall the last time I even did.

I've heard some guys say they don't tolerate short trips due to not getting enough heat in them too regen-but haven't heard any first hand data to support this.

2013 marked mostly interior and emissions updates. There were 8.4 radio quirks when they came out but most everything has been reflashes and/or a radio replacement and stuffs been solved.

I plan to own mine for 10-15 years, so I do take care of it. But it's a joy to drive/use.
Good luck.