Like Tony said, do the free travel mod for sure. Do your springs have the 1" spacer installed? If so, that might be why yours is sitting a bit higher. Mine are 5305 springs also but I'm not using the 1" spacer. Mine has the free travel mod but I can't remember how far my axle is from the frame. I can find out if you need it.
If you find out they don't have the spacer installed you can always trim off a couple dead coils to get a lower drop for the back without sacrificing ride quality. One of the nice things about the 5305's.
Mike