To make the sauce: in a saucepan, combine all the sauce ingredients and ½ cup water; mix well.
Bring to a simmer over medium heat; cook uncovered, stirring occasionally, until about 2/3 cup remains (about 30 minutes); let cool to room temperature.
Lightly brush both sides of the steaks with vegetable oil and season generously with salt and pepper.
Grill the first side of the steaks directly over high heat for 6 minutes; turn the steaks over and cook the second side for 5 minutes; continue to cook the steaks to desired doneness.
Remove steaks from the grill; season again with salt and pepper; let rest for 3-5 minutes.
You can serve the steaks whole or cut the siroloin strips and tenderloins away from the bones, then cut the meat into ¼-inch thick slices.
Serve warm with barbecue sauce.