There are new optionsfor /etc/resolv.conf in AIX 6.1 (not in 5.3):

Enables you to specify the initial timeout for a query to a nameserver. The default value is five seconds. The maximum value is 30 seconds. For
the second and successive rounds of queries, the resolver doubles the initial timeout and is divided by the number of nameservers in the
resolv.conf file.

Enables you to specify how many queries the resolver should send to each nameserver in the resolv.conf file before it stops execution. The
default value is 2. The maximum value is 5.

Enables the resolver to use all the nameservers in the resolv.conf file, not just the first one.