Sorry, but your post is confusing to read (for me). Not using code/quote tags is also problem. It's not clear what exactly is the problem. From what I have understood,
1. sudo command is not working for you (for your username)
2. you created a test account 'manageruser' but it would not work even with that user account
3. some commands seem to work. For eg. manageruser ALL=(ALL) /sbin/lspci
4. some commands esp aliases don't work. For eg. manageruser localhost=(ADMIN) NOPASSWD: DUMPS, SHUTDOWN, PRINTING
You can verify that,
1. your users are members of group wheel (or sudo)
2. relevent line (eg. %wheel ALL=(ALL) ALL) is not commented out.
3. There are no typos or other mistakes in the file. For example,
a) It's Cmnd_Alias not Cmd_Alias
b) The commands should be comma seperated. "Cmd_Alias SHUTDOWN= /sbin/shutdown /usr/sbin/halt /sbin/reboot"
4. In the line "manageruser localhost=(ADMIN) NOPASSWD: DUMPS, SHUTDOWN, PRINTING", ADMIN is runas alias. Have you defined it?
Post your /etc/sudoers file (wrapped in code tag ofcourse
. It would be easy to see if there are any mistakes in that file. Have you gone through Sudoers Configuration