Remove roast from pan; pour drippings into bowl. Let stand for 1 minute; skim fat. Spoon 4 Tbsp. drippings back into pan. Place pan on 2 burners set to medium-high. Add 4 Tbsp. flour and whisk for 3 minutes. Add 3 cups apple cider, whisking to scrape up browned bits. Lower heat to medium; cook for 15 minutes or until gravy thickens. Strain, season with salt and pepper, and serve.