What is the smoker temp at? How long did it take to get to an IT of 136?
When to Wrap is up to you. The general concensus around here is a Butt or Brisket tastes good with about Six Hours of Thin Blue Smoke. This also happens to coincide with the meats IT stalling at 150 to 170°F so good time to Wrap and push through. Ribs, 2-3 hours there is good smoke flavor, ok to wrap. Chuck, anywhere from 4-6 hours of smoke is good.
Wrapping earlier will just give some less smokiness but will not harm in any way. Then there are the guys like me that frequently don't wrap and add smoke the entire cook, 10 to 20 hours, with great result.
An IT of 140°F is Medium done. An IT of 160° is Well Done, gray no pink at all...BUT...If you plan to Pull the Chuck, at 160 it will cut or slice but will not likely pull. The Collagen Connective Tissue does not start to breakdown until an IT of about 130 and does not go quickly until the IT reaches 160°F. Even then it still takes Time. We usually will not see Pull Apart tender until the IT reaches 200°+...JJ