IOS RADIUS Authentication

Not sure what documentation you referenced to about the RADIUS attributes for privilege level assignment but the ones I found use the syntax "shell:priv-lvl=XX". See link below. Your example uses "shel:priv-lvl=XX". However through some testing I have done ACS 5.3 and IOS 15.3.3.M on a 2900 I have found simply “priv-lvl=XX” is enough to get the correct privilege level assignment. I went so far as to test with “adadlf:priv-level=7” and the correct privilege level was assigned just fine. I didn’t test with 15.1 and a 2800 but though it was an interesting discovery.

http://www.cisco.com/c/en/us/support/docs/security-vpn/remote-authentication-dial-user-service-radius/13860-PRIV.html