Is it possible that the cakes weren't cooked well enough? Maybe an undercooked cake would result in a gummy texture. (I've made this Lemonade Cake -- twice, already! -- and I haven't had a problem with it being gummy at all!) Check your oven temperature with an oven thermometer. I finally did on mine -- it was 50 degrees too low! -- and it's made all the difference in baking.
"In all our woods there is not a tree so hard to kill as the buckeye. The deepest girdling does not deaden it, and even after it is cut down and worked up into the side of a cabin it will send out young branches, denoting to all the world that Buckeyes are not easily conquered, and could with difficulty be destroyed." - Daniel Drake, 1833