Add all ingredients except cayenne pepper to a medium saucepan; stir until well combined. Place over medium heat and bring to a gentle boil; reduce heat and simmer, stirring often, until thickened enough to coat the back of a spoon, 15 to 20 minutes. Remove from heat and let cool 15 minutes.
While the BBQ sauce cools, carefully trim any silver skin from the tenderloins using a sharp knife. Cut trimmed pork into 1 1/2 inch cubes.
Combine pork cubes and 3/4 cup of the BBQ sauce in a medium bowl; stir well to coat. Cover and refrigerate at least 3 hours and up to 24 hours. Transfer remaining BBQ Sauce into an airtight container and refrigerate.
To Make the Pork Kabobs
When ready to cook, drain off and discard the pork marinade. Thread marinated pork cubes onto 8 skewers, taking care to not overcrowd them. Let stand at room temperature while you preheat the grill.
Preheat grill to medium-high. Place a bowl of the remaining BBQ sauce and a brush near the grill for basting.
Place skewers on a grill, leaving a little room between each one. Grill 8-10 minutes, basting with BBQ sauce every 2-3 minutes and turning to cook on all sides (until internal temperature reads at least 145℉ on an instant read thermometer).
Transfer kabobs to a platter and serve hot.
Notes
If you love BBQ sauce, consider doubling the sauce recipe to serve alongside. If you have any leftover, you'll find lots of uses for it!