Trim any silverskin off the tenderloins and transfer to a sturdy resealable plastic bag.

Make the marinade: Combine the red wine, garlic, and soy sauce in a small mixing bowl and whisk to combine. Stir in the chopped rosemary and the pepper. Slowly whisk in the olive oil; whisk until the mixture is emulsified. Pour the marinade over the meat and refrigerate for 8 hours, or overnight.

When ready to cook, start the Traeger grill on Smoke with the lid open until the fire is established (4 to 5 minutes). Set the temperature to 450 degrees F (or High) and preheat, lid closed, for 15 minutes.

Remove the tenderloins from the marinade (discard the marinade) and pat dry. Knock off any pieces of garlic or rosemary. Season generously with freshly ground black pepper and less generously with coarse salt.

Arrange the tenderloins at a diagonal to the grill grate and sear, turning with tongs as needed, until well-browned on all sides, 3 to 4 minutes per side. Continue to cook until the tenderloins reach your desired degree of doneness, 15 to 20 minutes total for medium-rare (135 degrees F on a meat thermometer). Let the meat rest for 5 minutes before slicing on a diagonal. Garnish with rosemary sprigs, if desired.