4.10s seem to be the popular gear whether for auto or manual. I dont think Ive heard of anyone yet going 3.73s in an auto. The stock gears are 3.55 so I really doubt youd ever notice a difference. Personally the T-lok is unquestionable to me. I dont know what Ford was thinking by not putting one in a car like this. If you upgrade the gears, I would defintly go with the T-lok. You're going to lose a lot of rubber if you dont, and that back right tire is going to break loose ALOT. I dont think I have to go into how dangerous that would be.
Keep in mind the associated HP loss with shorter gears. Someone at TMS reported a 10 rwhp loss with 4.10s in a v6 auto. For the torque, more than acceptable in my book.