I STRONGLY recommend that every new cake decorator purchase at least one book: The Cake Mix Doctor, by Anne Byrn, ISBN-10: 0761117199. You can get it online for under $5 from half.com including shipping. It doesn't matter if the book is new, because you'll end up getting "batter spatter" on the pages from all the fabulous recipes!
My family, friends and neighbors say my cake is the best cake they've ever tasted, and MOST of my cakes are from doctored cake mixes using recipes from the book above. In the first chapter (worth the price of the book for this chapter alone), Cake 101, Anne talks about pudding-in-the-mix cake mixes (Betty Crocker and Pillsbury) and Duncan Hines (NO pudding in the mix). She recommends:
"1st--don't use a mix with pudding inside if you're following a recipe that calls for instant pudding as an ingredient, and many in this book do."
"Second, cake mixes with pudding will be heavier, and very moist. If you want a light layer cake and are planning on placing a filling between the layers and then adding frosting, they're not your best bet. The bottom layer will be quite wet."
"Last, pudding cakes tend to shrink upon cooling. This may or may not.... bother you."