preheat oven to 375F.
Place pork in a shallow roasting pan or grill pan and pat dry with a paper towel.
Rub all sides with olive oil.
Season with salt and pepper on all sides.
Sear each side over high heat for 2 minutes per side, 10 minutes total.
While searing, make your sauce. In a medium bowl, stir together the 1/2 cup orange juice, vinegar, marmalade, and cranberry sauce.
Place seared pork in a large roasting pan and pour sauce over the pork.
Cook for 60-80 minutes or until internal temperature reaching 140-145 in the most central part of the pork. Baste every 20 minutes in orange juice mixture.
Remove from oven and place pork on a foil tented plate to cool/rest for 10 minutes.
While pork is resting, add remaining 1/4 cup orange juice to the juices left over from cooking. If your roasting pan is stovetop safe you can just keep all the sauces in the pan or if not, add to a saucepan.
Bring sauce to a boil and then reduce to a simmer while pork rests.
Slice and serve pork, drizzled with more sauce and garnished with orange slices and fresh cranberries.