Had the same problem and did all the things that you mentioned.
First, see if your repair receipt is itemized to include the replacement
of the timing belt as a warranty should accompany the repair if the belt
does go out in the future. Have your head gasket checked. That is
the only repair that I authorized to my 2006 above and beyond
everything else you listed. Haven't had a problem with it since. Hope
this is helpful but, if the problem now originates with the head gasket,
be prepared to shell out enough bucks to make you question whether
this car was such a good deal when you bought it. Replacing the
thermostat, water pump, head gasket, radiator, and timing belt ran me
about $2,600.00, all tolled. Hope this helps to explain yet another
possibility and that it is the last major repair you experience with
ownership.