I’m really at wit’s end trying to find an answer because I would like for your cake to come out right…specially, since you’ve already done the recipe thrice. This is the exact same recipe I’ve been using. I’m thinking it’s a toss up between overbeating the batter and the bake time. Ovens behave differently from each other. I’ve experienced quite a number of baking disasters following the bake time in certain recipes when my oven actually needed less time than what’s called for in the recipe. And don’t be tempted to open that oven door until the minimum bake time has elapsed.

Here’s a site you might want to check out which I find very helpful: http://www.theeveninginn.com/recipearticledisplay.aspx?article=77&name=Making%20Cakes