Prepare your grill. Turn all burners on high and let heat up. Scrape grates clean. Oil if needed. Turn one half of grill burners to low heat. Turn the other half off. Close the lid.
Meanwhile, whisk together 1/3 cup of the strawberry preserves, 1/4 cup of balsamic vinegar, the oil, one teaspoon of salt, thyme and black pepper. Place the tenderloins in a gallon-sized zipper bag and pour the marinade over the pork. Allow to marinate for about 20 minutes. If marinating overnight, keep the bag in the refrigerator until ready to grill.
In a small bowl, whisk together the remaining 2 tablespoons of strawberry preserves, the 1 tablespoon of balsamic vinegar and the 1/2 teaspoon of salt. Set aside.
Remove the pork from the marinade and discard the marinade. Place the tenderloins on the hot side of the grill and grill for about 5 minutes per side.
Transfer the pork to the side of the grill where the burners are turned off. Continue grilling until the internal temperature reaches 145 degrees F. This should take 25 - 30 minutes. Baste the pork a couple of times with the strawberry preserve and vinegar mixture while it's finishing on the grill.
Remove the pork to a clean cutting board and tent with foil. Allow to rest for at least 3 minutes. Slice and serve.