I've checked your configuration and it looks good. It is open to allow inside hosts to ping servers on the outside due to following commands in-
access-list acl_out permit icmp any any echo-reply
access-group acl_out in interface outside
However as you mentioned that you are not, could you enable "debug icmp trace" on PIX and then try to ping outbound .. syslogs will also be helpful. Pass on the outputs please.
Regards,
Vibhor.