In a cup or bowl, add in the vinegar and chicken stock. Stir to combine and set aside.
Season the roast all over with salt and place in slow cooker.*
Throw in the jalapeños and garlic.
Pour the vinegar mixture over everything.
Cover and cook on low for 6-8 hours, until the beef comes apart easily using a fork.
Using two forks, shred the beef.
Keep warm until ready to devour.