Season the pork butt with the salt and pepper and place into a 7 or 8 quart slow cooker.
In a medium bowl, stir together the orange marmalade, chili sauce, vinegar, soy sauce, and garlic.
Pour the sauce mixture over the pork butt.
Cover the cooker and set the cooker to high for 6 hours.
After the 6 hours is up, remove the pork butt to a large dish. Cover and allow to rest for 15 minutes.
Ladle 3 cups of the sauce remaining in the cooker into a saucepan.
Simmer the sauce over medium heat.
In a small bowl stir together the cornstarch and water.
Add the cornstarch mixture to the saucepan, stirring until the sauce thickens.
Shred the pork with two forks, and pour the thickened sauce over the pulled pork.
Season with additional salt and pepper to taste, if desired.
Serve on buns with additional Thai sweet & spicy chili sauce, if desired.