Preheat your Yoder Smokers YS640s Pellet Grill to 300ºF and set up for smoking.
Fill an A-MAZE-N Tube Smoker with hickory pellets. Lay on the main cooking grate on the left side of the grill. Light the end with a torch. Close the lid and let the flame burn out.
Combine all there ingredients for the sauce. Whisk well to combine. Transfer to a squeeze bottle.
Squeeze a little of the sauce on the chuck roast and spread in a thin layer that covers the whole roast. Season generously with the Cattleman’s Grill Road House Beef Seasoning.
Transfer the roast to the second shelf of the smoker. Smoke until a dark bark is formed, about 3 hours.
Slice half of your onion into thin slices. Dice the other half fairly small.
Lay out two sheets of heavy duty foil on top of one another. Place the thin sliced onion in the center (save the diced onions for the sandwiches). Lay the chuck roast on the onions. Pour about 1 cup of the sauce over the roast. Wrap tightly in the sheets of foil. Return to the smoker.
Continue cooking until the beef will easily shred apart. The internal temperature will be over 205ºF. This will take an addition 1-2 hours.
Remove from the grill. Rest for about 30 minutes.
Place the chuck roast on a cutting board and chop with a knife. Return the chopped beef to the foil and toss with the liquid left in the foil.
To build a sandwich, top the bottom bun with a generous helping of chopped beef. Place the diced onion and pickles on top of the beef. Squeeze more of the sauce over the top. Finish with the top bun.