Mix root beer, brown sugar, enchilada sauce, and garlic salt in a heavy duty gallon-size ziplock bag. Add the pork to the bag and put in refrigerator to marinade for a few hours or overnight.
Place roast (fattiest side up) and sauce in crock pot and cook on low for 11-12 hours (or on high for 6-7 hours).
Pull the meat out and shred with 2 forks (or stand mixer). Return the shredded meat to the crock pot to cook on low for about 2 hours.