Rawr, the multi-faceted simulation tool, has had a developer working on the DK tank module for a while now. It has just been updated to reflect the 3.22 changes also.
Rawr also works for tankadins, bears and prot warriors.
This is a fairly big tool, so I can’t say for sure which features to trust yet, but it has been improving a lot with each patch. You can search for known issues, by filtering for ‘tankDK’. You’ll see its avoidance calculation is still being tweaked, for example.
Dec 16th: the lead developer has contributed a guest post for pwnwear.
Learn how to use Rawr, for dps.
If you want to simulate threat, the best tool is Kahorie’s.