I have been baking my Grandma's Chocolate Cake for several years now. When I first started making it seven yrs ago, it used to sink in the middle when I took it out of the oven. Turns out I wasn't baking long enough. Rookie mistake. Fast-forward to a few months ago. . .all of a sudden, it will sink toward the end of its baking time. It looks perfect one minute, then I will look in the oven to see a huge sinkhole in the middle of my cakes. Then I will have to bake a whole other recipe(s) so that it's tall enough. . .it'd only be a little over 2" high after cutting the two layers and putting them together! I have tried using butter instead of veg short which does seem to help a LITTLE, switched from Hershey's to Ghirardelli cocoa powder?, convection vs. conventional, the soda is fresh and so is the powder. I can't figure it out. Could it be the change in seasons??? HELP! I have to bake a wedding cake in chocolate for Saturday! THANKS!

check your oven temperature. Too much leavener will cause the cake to sink too.

Handy cake trouble-shooting charts:

http://tinyurl.com/2p5bdu

http://tinyurl.com/32goqe

http://tinyurl.com/6c745g

HTH