Trim short ribs of any silver skin and pat dry with a paper towel. Season ribs on all sides with salt. Add oil to Instant Pot and set to saute. Once oil is hot, add ribs to hot Instant Pot and sear until dark golden brown on all sides, 3 to 4 min. per side. Transfer ribs to a plate and add garlic, Guajillo, and tomato paste to Instant Pot. Stir 1 to 2 min., or until toasted and fragrant. Stir in milk, barbecue sauce, and lime juice. Turn off saute function and add ribs back to Instant Pot, turning to coat in sauce. Place lid on Instant Pot, make sure vent is closed, and set to pressure cook on high for 35 min. When finished, allow Instant Pot to naturally release pressure by leaving it undisturbed for at least 20 min. Transfer ribs to a platter for serving. Set Instant Pot to saute to reduce sauce, stirring to emulsify until sauce has thickened slightly. Spoon sauce over ribs and garnish with parsley.