A new one showed up in Kent a few (3, maybe 4?) months ago, and I finally got around to trying it on one of my trips down there. It's on the southeast corner of the intersection of SE 256th & 104th Ave SE, right where 256th turns into Kent-Kangley Road. It's just on the east side of the Chevron station.
They serve tacos, burritos, quesadillas, sopitos, mulitas, tortas, and carne asada. They probably serve other dishes too, but that's what I remember off the top of my head. Don't remember all the meat choices, either, but do recall asada, pollo, lengua, tripa, and I believe carnitas. I'm sure there were other meats available; unfortunately I wasn't at my most observant.
It's in a converted bus, and there is seating and heating inside, so that's where The Dude and I ate. He had tacos with asada, I had sopitas with pollo, washed down with agua fresca de jamaica.
This was my first visit to a taco truck, so I don't really have anything with which to compare it. For the record, though, we both enjoyed our meals very much. I was pleasantly surprised by how flavorful the pollo filling was. The Dude was full, I couldn't finish all mine, and we got away for under $10. We both agreed we'd be back.