What do you see under ACS > tacacs authorization logs. If you have already defined the command set and hitting the right one and still failing then most likely the format/syntax you have defined and the format/syntax the NAS device sending do not match.
You can also turn on debugs and check what NAS is sending to ACS.
debug tacacs
debug aaa authorization
term mon
You may also go through the ACS 5 command authorization configuration example.
http://www.cisco.com/c/en/us/support/docs/security/secure-access-control-system/113590-acs5-tacacs-config.html
Regards,
Jatin Katyal
*Do rate helpful posts*
~Jatin