Prepare a gas or charcoal grill for indirect cooking (leaving one burner unlit or banking coals to one side). Put a disposable drip pan on the unheated side. Preheat grill to medium-high heat (375°F to 450°F).

Stir together garlic powder, onion powder, chili powder, paprika, and salt in a small bowl. Rub mixture all over pork.

Whisk together balsamic vinegar, honey, and mustard in a small saucepan. Bring to boil over high heat; reduce heat and simmer, uncovered, until reduced to about 1/2 cup, 10 to 15 minutes.

While glaze simmers, oil grill grate and arrange pork on grate directly above heat source. Grill, covered, turning every two minutes, until seared on all sides. Move pork to unheated side of rack and close grill lid. Continue grilling, occasionally turning and brushing with glaze, 15 to 18 minutes, or until an instant read thermometer inserted in thickest part registers to 145°F. Transfer pork to cutting board, loosely cover with foil and let stand 5 minutes before slicing.