Heat oil in a heavy large pot over medium high heat. Brown roast, letting it sit undisturbed on each side until it is more easily removed from the pan, creating a nice golden crust on the exposed edges (this adds flavor, do not omit). Remove to crock pot large enough to hold the roast.
Deglaze pan, turn off heat of pan but while still hot, add the broth to the pan and stir until the bits on the bottom of the pan are cleaned off. Add broth and browned bits to crock pot.
Add salsa, garlic, brown sugar and soy sauce to crock pot. Cook until meat falls apart, about 4-6 hours on high or 8-10 hours on low, depending on your crock pot (another good reason to do ahead of time, if the meat doesn't fall apart, keep cooking it in the crock pot).
When meat falls apart, remove from the crock pot in batches, shred using two forks and put in a container, discarding fat (this is the majority of the preparation time).
Skim fat from the juices left in the crock pot, then pour the juices over the shredded meat in the container. Refrigerate overnight (the meat will soak the juices back up if you do this) or freeze.
When ready to eat, reheat in a pan on the stove and add lime juice and cilantro. If frozen, thaw in refrigerator or microwave.
Can serve with tortillas and traditional fixings like lettuce, tomato, cheese, salsa, avocado, sour cream and additional salsa, or it's really good with salad greens and black beans.