Combine pork, orange juice, and salt in the slow cooker. Set on low and cover.
Bring a small saucepan of water to a boil. Remove from heat and add chiles. Press down to submerge in the water and let soak 15 minutes.
Remove chiles from water and place in a blender along with the remaining ingredients and 1/2 cup of the chile soaking liquid. Remove the lid and hold a towel you don't mind getting dirty over the top of the blender. Blend on high until smooth.
Pour chile mixture into slow cooker and stir to combine. Cook on low for 8 hours or on high for 4 or until pork is tender and falling apart.
At this point you can remove pork from the sauce and shred then mix a bit of the sauce back into the pork. If you want to take an additional step you can turn the broiler to high and place the shredded meat onto a foil-lined baking sheet. Place under the broiler until the edges are crisp, about 2-3 minutes. Mix with about a cup or two of the sauce and serve.