What do I do next with my VSC and check engine lights?

So I have had my VSC check engine light on
in my 2005 Highlander for the past few
months. I changed the gas cap and
unplugged the battery to reset. It came back
on. At one point I reset the battery again and
drove on the highway for about 7 hours. The
lights did not come back on. The next day I
started driving around town, they came back
on. The same thing happened on the way
back. I also found a vacuum hose that was
loose. Reconnected it and reset the battery. It
came back on. I have now taken it to a
mechanic and he says he has to replace both
catalytic converters!! $1700. From what I read
here there has got to be another answer for
this. Just doesn’t seem right. Thoughts?
Suggestions?