A new Read Dead has supposedly been in development the last three and a half years. A rockstar dev has leaked new information on an AMA thread on reddit.
Red Dead Redemption is one of my all time favourite games, the multiplayer is awesome. It could be shown at this years E3 guys, bring on the hype train. Link below...
http://www.technewstoday.com/27515-a-sequel-to-red-dead-redemption-very-much-a-possibility-after-employee-drop/
http://www.dsogaming.com/news/red-dead-redemption-2-legends-of-the-west-rumored-to-be-unveiled-at-e3-will-be-multiplatform/
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I doubt it will have been in development for three years, maybe one and a half at best. That time is also probably just focusing on what he story will be and character design