You could get 3.73's for 09, but primarily they switch to the 3.55 for better fuel economy.

3.55 would be better if you are going to be using it for travel to and from work.

I like 3.73 gearing as the best all round ratio for my purposes.

 

Just bought an '09 F350 DRW 6.4 myself. Thanks for this info. Good stuff!

 

Not too long ago somebody posted a nice detailed narative of what to look for and to look out for on the 6.4 trucks...I have a friend now looking to buy one also. Where can I find that post for him to read? can it be reposted in this thread?
Thanks for helping find it.