I like the new savetostandby bootconfig flag, which will cause config changes to be sync'ed between the primary and secondary CPU modules. Its also worth double-checking that your timezone and other clock settings are the same on both CPU modules.
I haven't ever used it, but I think the ha-cpu bootconfig flag is what enables full l2 redundancy. I seem to remember that there are specific things you need to be aware of when running in ha-cpu mode so be sure to read all of the release notes and other documentation for your software release.
As I understand it ha-cpu provides l2 redundancy in the 3.5 code branch, and l2/l3 redundancy in the 3.7 code branch.