There are two ways you can do this recipe, I have tried both and both versions work out well:

We have a PitBoss smoker and tend to use that for this recipe:

Season chicken thighs w/ salt, pepper, and garlic. Set smoker to 230* and grill thighs at until they reach an internal temp of 160*. Transfer the thighs to foil and drizzle over 1/4-1/3 cup of balsamic vinegar (depending on how many you make at a time). Increase smoker heat to 250* Cook until chicken reaches a temp of ~195* (roughly 1 more hour) or until chicken pulls apart w/ a fork.

You can do the same thing in the oven if you do not have a smoker. Grill the thighs until done, transfer to foil, cover w/ balsamic vinegar, then leave in oven at 250* for ~75 minutes until chicken pulls apart w/ a fork.