How can I make barbacoa like street taco vendors?

I’ve made barbacoa a couple times with 5 lbs if bistek. It hasn’t come out like a typical street taco vendor, dark and soft. Mine is soft but not dark and lacks the same flavor no matter what recipe I use.

How do I get the meat to be that dark and soft? Is it a different cut? Do you have a specific recipe?

bon appetit