Joann I have found in my shop that when I bake and it has a gooey center... to stop this, I place a metal flower nail in the pan directly in the center, flat head down (after greasing and flouring the pan) hit it with a shot of cooking spray and then just fill the pan with batter. Make sure the nail doesnt turn over.
When you turn the banana bread out the nail is on the bottom just let the bread cool for a bit and place a flat blade knife under the flower nail and pull it right out.
No more gooey centers.
I also do this on sheet cakes that are larger than 11x15. 2 of them 3 inches apart in the center of the pan.