Place meat in side slow cooker. Slice onions and peppers (remove stems too) and put into pot.
In a bowl whisk together dry gravy mix, pepperoncini juice and broth together. Then pour into the pot.
Sprinkle garlic salt and pepper on top, add garlic and close lid to cook.
If defrosted cook on low for 6-8 hours, high for the same time if frozen solid.
Best results if you are able to flip the meat after hour 4, then remove bones and fat and shred meat at hour 6. Then leave shredded beef inside juices 30 min-1 hour before serving to soak up juices.