Bread-Bakers v113.n001.3

Two thoughts:

1. Vent the oven during the last 5 or so minutes to let humidity escape.

2. Bake longer at lower temperature to drive more moisture out of the 
loaf. You can even try starting at a high temperature and dropping 
the temperature mid-way through baking.

Are you getting as much oven spring as you expect? Are you confident 
your baking stone is thoroughly preheated? Are you confident that you 
are proofing the shaped loaf the right amount?

Happy baking,
Allen
San Francisco