The San Francisco 49ers and Frank Gore have agreed to a three-year extension worth $21 million, a source familiar with the deal told ESPN NFL Insider Adam Schefter. The contract contains $13.5 million guaranteed, the source said. Gore's agent, Drew Rosenhaus, met with the 49ers' front office Monday and Gore said earlier Tuesday that Rosenhaus categorized as a productive sitdown. Read more: http://espn.go.com/nfl/story/_/id/6...cisco-49ers-agree-3-year-21m-deal-source-says