There's been a taco truck parked just off Broadway on 29th (towards the discount grocery store) for the last few weeks.
Tacos are $1.25, tortas $4, and there are also burritos and something else. Standard meat choices, plus tongue and others I wasn't brave enough to try.
I chose an al pastor taco (being not terribly hungry). It came with wedges of radish and lime, and was very tasty! I'll definitely drop back in for more intra-meal snacks.
The truck says "taqueria barajita" (or something like that), and lists an address in the 4000 block of E 14th. Sounds like a prime taco truck location. Don't know why they relocated, but they get a good flow of customers, even at 11am on a holiday, so it must have been a good choice...