Place meat on rack in roasting pan; insert meat thermometer. Roast in slow oven (300 to 325°) until meat thermometer registers 170°, or about 40 to 45 minutes per pound. Remove from oven and allow to stand about 20 minutes, then slice, saving juices.
Shake or beat together oil, vinegar, salt and pepper. Remove any excess fat and burned drippings from roasting pan