In a small bowl, mix together garlic powder, onion powder, sugar, thyme, allspice, black pepper, cayenne, salt and cloves. Reserve 1 teaspoon of mixture for potato salad. Press rub evenly into both sides of London broil and place in a resealable plastic food-storage bag. Refrigerate 4 hours or overnight.
Place potatoes in a medium-size saucepan and cover with lightly salted water. Simmer for 20 to 25 minutes until fork-tender. Drain and cut into bite-size pieces.
Place peppers and onion in a large bowl. Add potatoes. Cover with plastic wrap and let cool on counter 15 to 30 minutes.
Meanwhile, in a small bowl, whisk together mayonnaise, sour cream, milk, salt and reserved teaspoon of rub. Fold into potatoes and peppers. Cover and refrigerate for at least 4 hours.
Heat broiler and coat a broiler pan with nonstick cooking spray. Broil steak 6 minutes. Turn and broil 5 to 6 minutes more or until internal temperature registers 135° on an instant-read thermometer for medium-rare. Let rest 5 minutes before slicing.