I would prepare a counseling statement that references one or two recent examples of his unwillingness to promptly execute orders, tasks, or directives. Have your chain of command review the counseling statement prior counseling the Soldier. This will ensure that you have support should you have to elevate the situation.
Inform the Soldier that failure to promptly execute an order in a professional manner to the best of his ability, or any whining about the order will be dealt with by refering the matter to the chain of command for resolution up to and including UCMJ action as appropriate. Have the Soldier read his latest set of promotion orders as they relate to obeying orders.