I've set up sla monitor per Cisco Document ID: 70559
This morning it failed over to the backup link like it should.
However, when the primary ISP link was restored it was not reinstalled as the primary default-route. I disconnected both primary and backup links from the ASA, waited 60 seconds and then reconnected the primary link. Route still did not come back up. I reconnected the backup link and it was installed as the default-route.
I had to remove the SLA code to get the primary ISP route restored.
I also turned on SLA debugging, but was not getting ANY msgs.
Edit: Does ip verify reverse-path break SLA?
The 5510 is a security plus in case it matters.