Finely mince tender lower 3 to 4 inches of lemongrass for about 3 tablespoons. Mix with garlic, shallot, fish sauce, soy sauce, sugar, oil, lime juice, and pepper.
Coat chops with marinade; cover and refrigerate 30 minutes, included in prep time.
Heat outdoor grill to about 400°F with cooler indirect area; clean grate. Lift chops, letting excess drip; discard used marinade.
Grill 4 to 6 minutes per side until patchily browned and thickest meat at least 145°F. Move to indirect heat if edges darken too quickly.
Rest at least 3 minutes; serve with cooked lemongrass seasoning clinging to meat.