In the insert of a slow cooker or in a pressure cooker, add pork shoulder, beer, garlic powder, cayenne pepper, chili powder, pepper, salt, cilantro paste and lime juice. Stir to combine. Set slow cooker to low and cook for 8 to 10 hours, or 80 to 90 minutes in the pressure cooker. Remove pork with slotted spoon to a separate serving dish. Using two forks, pull apart the pork shoulder until all of it has been shredded. Set aside and keep warm.