Trim fat from roast and cut it to fit into a 4 quart slow cooker if necessary. (I find that its usually not!).
Combine caraway seed, marjoram, salt and pepper and rub over roast.
In a large skillet, brown roast on all sides in the hot oil and drain off the fat. Place meat in the slow cooker.
Add the water to the same skillet and bring to a gentle boil over medium heat, stirring to loosen brown bits from bottom of skillet.
Pour skillet juices and vinegar into the slow cooker. Cover and cook on low setting for 8-10 hours or high setting for 4-5 hours.
Remove meat from slow cooker and keep warm.
For the gravy, skim the fat from the juices left in the slow cooker and measure out 1 and 1/4 cups of these juices (Add water to make up the difference if necessary). Combine sour cream or yogurt and cornstarch and gradually stir in the hot juices.
Transfer the gravy to a saucepan and cook over medium heat until thickened and bubbly, stirring constantly. Cook and stir for an additional 2 minutes.
Serve the gravy with the pork roast and hot cooked potatoes if desired.