In a blender, combine tomatoes, brown sugar, vinegar, garlic, salt, oregano, paprika, and red pepper. Blend until smooth.
Place pork in crockpot. Top with onion. Pour tomato mixture over pork and onions.
Cover and cook on high 4 to 5 hours or on low 8 to 10 hours, until pork is very tender.
Remove pork from cooker; cool slightly.
Pour sauce mixture into medium bowl. Remove onions from sauce, and set aside. Skim fat from sauce. Keep sauce warm.
Shred pork with 2 forks, and return to cooker. Add onions and 1 cup of sauce. Cook on high for 15 to 30 minutes, or until hot.
To serve, spoon 1/2 cup of pulled pork onto bread or a roll. Top with sharp cheddar cheese. Serve with remaining sauce for dipping.