How to configure TACACS+ on Cisco ACS 5.3 for authenticating administrative users on LTM 11.2.0?

Sure. Here's our remote role config for our administrator role:

auth remote-role {
    role-info {
        /Common/GW_Administrator {
            attribute F5-LTM-User-Info-1=adm
            console tmsh
            line-order 1
            role administrator
            user-partition all
        }

Your TACACS+ server config should look something like this:

auth tacacs /Common/system-auth {
    protocol ip
    secret ******
    servers { 10.1.1.1 10.1.1.2 }
    service ppp
}

The ACS group that you wish to have administrator access will need to be assigned that shell profile you created in ACS. But the ACS group name will have to match verbatim what the remote role name is (in our case, it's GW_Administrator).