For me the only way to cook a pork tenderloin is to braise it. If you have never done it, I recommend trying it just once and see what you think.
Method:
Take your pork tenderloin and massage some oil all over it; I use peanut oil.
Liberally salt, probably more salt than you would think you need. Fresh cracked black pepper. A lot, but not nearly as much as the salt. That is all you need. If you want to add fresh herbs, it would be good here too, but oil, salt and pepper is all I use.
Then, get a thick cast iron skillet and turn the heat on as high as it will go. Leave it for a few minutes as cast iron takes a bit to heat up all the way. While you are waiting for it to heat up, turn the oven on 350 and open some windows and turn on some fans. When the skillet is hot, lay the pork in there, it is going to hiss at you quite loud and it will smoke quite a bit. However, don't touch it for two minutes. After two minutes, flip it over on the other side and let it sit for three minutes (three minutes this time because the pan is going to be a little bit cooler). After three minutes, flip it onto one of it's edges for two minutes, then the other edge for two minutes, and then in the oven for 40 minutes.
If you have never tried braising a pork tube, I suggest you try it just once, it is so freakin good.