RT migration from 3.0.9 to 3.4.1

I have an older version of RT running under PSQL, I have 3.4.1 running
under MySQL-what is the best way to migrate all of the tickets to the
newer version of RT? I do not necessarily need to migrate the queues,
groups and so-on, just the tickets.

What is the best way to do this?

Has anyone done anything like this before?