In a large saucepan over medium heat, toast the chilis for about 5 minutes, turning chilis occasionally until the chilis are pliable, lightly browned and aromatic. Then add oregano, cumin, and achiote paste, stirring frequently for about 30 seconds. Add the chipotle and sauce, chicken broth, vinegar, garlic, salt, and sugar and stir for another 60 seconds. Be sure to have all ingredients on hand and work quickly to prevent the spices from burning. Remove from heat and let it cool.
Scrape contents of saucepan into a blender or food processor and blend on high speed until very smooth, about 1-2 minutes. If the paste seems thick, add a bit more broth. Scrape down the sides as necessary.
Using a sharp knife, remove the tough skin and some fat from the pork shoulder. It is fine to have some extra fat on the meat as it will render down and provide extra moisture and flavour when on the grill. Hand slice the pork shoulder into 1/2-1/4" thick pieces.
Place the pork shoulder in a large bowl. Then add the marinade and toss very well until the meat is coated evenly in the marinade. Cover tightly with plastic wrap and refrigerate for at least overnight and up to 24 hours, to allow the marinade to penetrate through the meat.
The next day, set the Big Green Egg on indirect heat at 175C/350F.
Slice the pineapple into 1.5-2 inch thick slices.
Using a trompo or a vertical skewer, first skewer 1-2 slices of pineapple on the bottom. Then carefully skewer the pork shoulder slices high on the vertical skewer, and finish with two slices of pineapple on top.
Transfer to the Big Green Egg and roast until the pork registers an internal temperature of 93C-95C/200F-205F. Be sure to check the temperature at different parts of the vertical skewer.
Let the pork rest for 15-20 minutes. Then vertically slice the pork directly from the vertical skewer or trompo.