Welcome to the site. Which light do you mean by the transmission light? What does it look like? Only time I ever had a slightly similar problem was when I got some kind of odd diesel during the very cold weather. Used to lose power and would correct itself when I turned off the engine and started up again. But it never cut out on me. Have you checked or changed the fuel filter (and banjo filter if you have one). The article on checking and clearing disgnostic codes should be easy enough to find in the downloads section of this site.
