Heat oven to 350 degrees. Grease bottom only of a 13x9 pan with shortening.
In a large bowl, beat all cake ingredients with electric mixture on low speed for about 30 seconds, scraping bowl. Beat on high for 3 minutes, scraping bowl. Pour into pan.
Bake 35 to 40 minutes or until inserted toothpick comes out clean. Let stand 5 minutes.
Pierce top of hot cake every 1.2 inch with long tinged fork, wiping form occasional to reduce sticking.
In large bowl, stir 1 cup of whipping cream, the whole milk, condensed milk, and rum until well blended. Carefully pour milk mixture evenly over top of cake. Cover and refrigerate about 3 hours (I have heard overnight is best) or until chilled and most of the milk has been absorbed into cake.
In chilled bowl, beat 1 cup whipping cream, 2 tablespoons rum, and 1/2 teaspoon vanilla with electric mixer on high speed until soft peaks form. Frost cake with whipped cream mixture. Sprinkle with pecans.
Store covered in fridge.