Usually you want the shoulder for slow cooked pork, but if you have to use loin, just realize it will be on the dry side. You might want to cook it a bit less.

I would probably find myself adding some bacon fat or other rendered fat to the tenderloin as it cooks, to make it less dry and give more flavor to the sauce. I agree with nutcakes about cooking it less too, as it will get hard if overcooked. I'd cook down the sauce, with everything except the browned meat added in, and then put the meat in towards the end til it's heated through, checking it every 5 minutes or so - I wouldn't expect it to take very long at all.

Why would you use such a relatively expensive cut in a recipe like this? It's the fat and connective tissue in pork shoulder that makes a dish like this tasty.