Do you like sirloin steak? If so, you should get a tritip. It's just a really well marbled sirloin that sometimes is a little more tender than a sirloin steak. Some people drive themselves nuts trying to find in their area, and after having many of them I would say generally speaking it's not THAT different than a sirloin steak. If you can easily get ahold of one give it a try, but don't go to great lengths if they are not plentiful in your region.
FMT, it's been about 50 years since I helped my dad cut and wrap beef and we never cut a side of beef in a way that produced a tri-tip, so I may be a bit off base, here, but it appears to me that the trip-tip is significantly different from a sirloin.
If you were sitting toward the rear of a heifer you'd be sitting on the sirloin. Well below that, just to the rear of the flank is where I think the trip-tip originates.
As I often say, "Working from memory here." It may not be difficult to prove me wrong.