In addition to your preset configuration, these commands are required on an IOS router or switch in order to implement command authorization through an ACS server:
aaa new-model
aaa authorization config-commands
aaa authorization commands 0 default group tacacs+ local
aaa authorization commands 1 default group tacacs+ local
aaa authorization commands 15 default group tacacs+ local
tacacs-server host A.B.C.D
tacacs-server key cisco123
http://www.cisco.com/en/US/products/sw/secursw/ps2086/products_configuration_example09186a00808d9138.shtml#backinfo