I have tried adding yogurt, pudding mix, sour cream, and tried different kinds of butter verses shortening and oil recipes. My cakes still come out a little dry. I do live in Florida. Would humidity be a factor? Thanks for any ideas.
You may be baking them too long - you can also use simple syrup on cake layers to keep them moist.
Do you freeze your cakes after they cool? I was in a seminar today with Buddy Valastro and he said that freezing your cakes help seal in the molecules that make your cake moist. I personally use the WASC recipe and don't skimp on the sour cream. I actually add in a little extra.
Sounds like you are over baking them.
Do you weigh your flour? When I do not weigh, I scoop and level of the flour, making sure not to pack the flour into the measuring cup.
Edited: Extra flour and/or over baking could be the culprit.
Take the cakes out of the oven about 2 minutes before it is completely done (or when there is just a few cake crumbs on the toothpick) and let it sit in the pan on a cooling rack for 10 minutes. Leaving it in the hot pan will cook it all the way. After 10 minutes remove from the pans and immediately wrap in plastic wrap and put them in the freezer.
That's what I do and everyone says how moist my cakes are.