Place the sliced onion into the bottom of the slow cooker. Rub the outside of the pork roast with salt, pepper and garlic powder. Pour Dr. Pepper over the roast and cook on low for 7-8 hours or on high for 4-5 hours.
The meat will be very tender and pull apart easily. Using 2 forks, shred the pork and place back into the juices. Add the BBQ sauce to taste. Allow cooking for an additional 30-60 minutes if desired.
Served on crusty rolls with coleslaw or cheddar and French fried onions if desired.