Lots of people use skirt just for fajitas, but I find it great as a steak. As mentioned, slicing correctly is EVERYTHING when it comes to tenderness.
I think that goes for tri-tip as well. I find that the thinner I slice it, the more tender it is. But that seems to go for most kinds of meat anyway (except jerky).
Tim - with that in mind, if you were to slice your tri-tip very thinly, you might be able to enjoy it without any side effects. It's also called "bottom sirloin" sometimes and it also makes a decent steak. In fact, if I don't ask my butcher for a whole tri-tip, steaks are what I get.
If it's sliced really thinly, tri-tip is even better than the shaved roast beef I use in sandwiches. It digests more easily too.