Prepare and bake cake mix according to box directions for a 9 x 13 inch cake pan.
While the cake is baking, combine pineapple with juice and 3/4 cup sugar in a medium saucepan. Cook over medium heat for 20 minutes until thick and syrupy, stirring occasionally. Pierce top of hot cake with fork at 1 inch intervals. Pour pineapple mixture over cake. Cool completely.
Beat pudding mix with milk until smooth. Spread pudding over cooled cake.
Whip cream until slightly thickened. Add confectioner's sugar and vanilla, and whip until soft peaks form. Spread over top of cake. Chill cake for 24 hours. Sprinkle with coconut and pecans just before serving. Refrigerate leftovers.