Layer sliced onion in the bottom of the slow cooker. Place pork roast on top of onions.
Mix together salt, pepper, garlic powder, and thyme - sprinkle on the roast.
Pour stock carefully around the side of the roast.
Cook on LOW for 5-6 hours, or high for 4-5.
30 minutes before the roast is done, mix together brown sugar, water, soy sauce, and balsamic vinegar in a small pot. On medium-low heat, bring the mixture to a simmer. Reduce by about 1/3 or until slightly thick. Set glaze aside.
When roast is done, take out of slow cooker and place in a roasting pan.
Heat oven to 450 degrees.
Pour 1/3 of the glaze over the roast and place in the oven. Continue to glaze roast every 5 minutes until glaze is used up.
Take roast out of oven, loosely tent with foil and let rest for 10 minutes.
Slice or shred with a fork. Serve with extra drippings.