First figure out your warranty. It's 5/50...7/70 depending on what's wrong.
Second, 2.5-3 hrs shop time to do a regen is robbery, so I'd sort that out before going further w that dealer, unless they did more than that.
Last, in general, LMLs are generally decent preforming emissions systems. No tell what the cause is from here, but they can handle more putting around than the LMM engine emissions. But you still have to drive it long/hard once in a while. These diesel emissions systems aren't completely idiot proof as we would expect with 21st century stuff.
If you can delete it, it will perform flawlessly, like an old pre 08 truck, if emissions testing isn't a concern.
You'll need a private shop not the dealer to do it, if you're not planning on doing it yourself. Check out diesel place.com to learn about deletes.