In a large, deep skillet, heat 2 tbsp. oil over medium-high heat. Season the pork with salt and pepper and brown on all sides, about 7 minutes; transfer to a plate. Pour off the fat.
Add the bell peppers, onion, garlic, sage and remaining 1 tbsp. oil to the pan and season with salt and pepper. Cover and cook over low heat, stirring occasionally, until slightly softened, 8 to 10 minutes. Add the tomato and broth to the pan and bring to a boil over medium-high heat. Add the port, cover and cook over low heat, turning the meat once, until an instant-read thermometer inserted in the center registers 145 degrees , about 40 minutes.
Remove the pan from the heat. Transfer the pork to a cutting board and let rest for 10 minutes. Slice into 1/4-inch-think pieces and transfer to a platter or plates. Meanwhile, place the vegetables and juices back on the heat and bring to a simmer; serve with the pork.