Combine 1 1/4 teaspoons crushed peppercorns and salt; rub over surface of roast.
Coat a nonstick skillet with cooking spray; place over medium heat until hot.
Add roast, and cook until browned on all sides, turning occasionally.
Transfer roast to a 4-quart electric slow cooker.
Add water to skillet; bring to a boil. Deglaze skillet by scraping particles that cling to bottom.
Pour water mixture over roast. Cover and cook on high setting 3 hours or until roast is tender.
Remove roast from cooker; set aside, and keep warm.
Pour pan juices from cooker into a small saucepan; skim fat from juices. Bring juices to a boil.
Combine sour cream and flour; add to saucepan, stirring constantly. Cook over medium-low heat, stirring constantly, until thickened and bubbly. Stir in remaining 1/4 teaspoon crushed peppercorns.