Combine all the ingredients except the pork in a blender or a food processor. Blend until smooth.
Place pork loin in a heavy plastic food-storage bag. Pour half the peach puree into the bag. Marinate overnight. Refrigerate remaining peach sauce.
When ready to cook, set a drip pan in the charcoal bed of the grill, with about two cups of water in the pan. Arrange coals around the pan, and add wood chunks atop the coals.
Place pork loin on the grill right over the drip pan, avoiding any direct convection from the coals. Baste and turn every fifteen minutes with the excess marinade that was with the meat. Cook until internal temperature reaches 155-160 degrees, about 60 minutes. Let stand for 10 minutes.
Heat the reserved peach sauce (not the batch that marinated the pork!) until it comes to a light simmer. Adjust with salt and pepper. Slice the pork about the thickness of two quarters and serve with the reserved peach sauce.