RichKid,
If you have fertilized both trees the same, and they are getting the same water and sun exposure, then I can only guess that the one that is sulking had less roots or has grown less roots since collection. My only suggestions would be patience, keep doing what you are doing, or maybe moving the sulking one to a little more shade (afternoon shade or dappled light all day). It may be stressed a little by too much sun and heat. But, if you already have it in those sorts of conditions, then patience.
Regards,
Martin