Lay tenderloins on cutting board with long side running parallel to counter edge. Cut horizontally down length of tenderloins, stopping 1/2" from edge so 1/2's remain intact. Working with one at a time, open up tenderloins, place betweem 2 sheets of plastic wrap & pound to 3/4" thickness.
Combine soy sauce, jelly, hoisin sauce, sherry, ginger, sesame oil, garlic, five spice powder & pepper into a bowl; mix well. Reserve 3/4 C marinade. Place pork in large zip lock bag & pour remaining marinade over pork. Turn to coat & refrigerate for at least 1 hour or longer or up to 4 hours.
Combine reserved marinade, ketchup & molassas in a small saucepan. Cook over medium heat until syrupy & reduced to 3/4 C, about 3 - 5 minutes. Reserve 1/4 C glaze for glazing cooks tenderloin.
A. FOR CHARCOAL GRILL: Open bottom vent completely. Light large chimney starter filled with charcoal briquettes (6 qts). When top coals are partially covered with ash, pour evenly over grill. Set cooking grate in place, cover & open lid vent completely. Heat grill until hot, about 5 minutes.
B. FOR A GAS GRILL: Turn all burners to high, cover & heat grill until hot, about 15 minutes. Turn all burners to medium high heat.
Clean & oil cooking grate. Pat pork dry with paper towelsm then rub with vegetable oil. Grill pork (covered if using gas) until lightly charred on the first side, about 2 minutes. Flip & brush grilled side of pork evenly with 2 tbsp glaze. Continue grill until lightly charred on second side, about 2 minutes. Flip & brush evenly with 2 more tbsp of glaze. Repeat flipping & glazing twice more, until pork registers 140 degrees F & is thickly glazed, about 4 minutes longer. Transfer pork to cutting board & brush with reserved glaze. Tent loosely with foil & let rest 5 minutes. Slice & serve.