Hmm. Most slide films these days are formulated with fine grain in mind, so you may have a hard time finding something that looks similar to Tri-X- depending on how you process your Tri-X. Leaving that aside, I'll second the suggestion of Provia 400. For slide film, it can be fairly grainy. As for color rendtion, well, that's pretty subjective; and of course, how the film is stored, exposed, and processed will all affect color rendition, too-as will the atmospheric conditions the film is shot in. I hope it isn't news to anyone here that color is so difficult to handle with precision in any photographic process. Ok, maybe I'm being too nit-pick-y or over the top about this, but my point is that there are so many factors here, and the over-all subjectivity of the results seems to dictate that you're just going to have try a few things and decide for yourself. Like many things we ask each other about here, this is one of those questions to which five photographers will give you five different answers, each with certainty that theirs is the last word on the subject.
So. For my own shooting, I find Provia 100F to be the most neutral, natural color slide film for general use under most conditions; however, it's pretty fine grained. Provia 400 is, to my eye somewhat weaker in terms of fidelity to the original subject color; but it does show more grain, and has roughly the same basic speed as Tri-X (if that's what you are looking for). It does offer a shadow of the pushability of Tri-X, but only a shadow. Color gets flattned out and looses punch as you push- but you do gain grain. This is pretty well true with all chrome material in my experience.
You'll really just have to do your own testing; let us know what you think when you find something you like.
