Combine brown sugar, lemon juice, molasses, vegetable oil, mustard, honey, chili powder, and garlic in a large bowl. Toss in shrimp to coat, cover, and refrigerate for 2 hours. Meanwhile, soak wooden skewers in hot water to prevent burning on the grill.
Preheat an outdoor grill for high heat and lightly oil grate.
Thread shrimp tightly on to skewers. Cook on the top rack of the grill for approximately 4 minutes, or until the shrimp turns pink on one side. Flip shrimp and cook for an additional 2 to 4 minutes, or until there are no signs of grey.
1 cup brown sugar
1 tablespoon lemon juice
1 cup molasses
1 teaspoon chili powder
1 tablespoon minced fresh garlic
1 tablespoon mustard
3 tablespoons honey
2 tablespoons vegetable oil
4 pounds large shrimp, peeled and deveined