Maybe try using a different oven. I bake mine most often in the convection oven. I bake there at 350 and for 25 minutes (it would be 35 minutes and 375 in the regular oven).
I have a roaster oven I'm going to be doing some baking in soon. My mom always had great results that way, but I haven't had a roaster until recently, when my glass bowl convection oven finally died and I thought I'd try something new.