'85 GT cooling problems

[ejfluhr@wc101.residence]

Sorry if this has already appeared on the list.  I had some problems with my 
mail, and didn't think it had gone out.

Hey all, I hope you can help me.
A few months ago, my radiator hose blew.  At the time, I noticed that the
coolant temperature gauge was extrememly high, maybe 7/8 of the way up.
Well, I think that was a symptom of a very weird problem.  Since that time,
the engine has never been as cool as it used to run.  When I bought it used, it
ran *extremely* cool, even at highway speeds the temp gauge would stay
only about 1/4 up, and the oil temp gauge never exceeded 130 Celsius.
Now, the coolant doesn't seem to stabilize at any particular temperature.  It
also doesn't seem to have any pattern of heating/cooling.  For example, I can
be running down the highway at 60 or 70 mph and the temp gauge stays about
2/5 of the way up.  Not as good as before, but acceptable.  Then, suddenly, it
will begin climbing rapidly.  Sometimes it goes up a little, then stabilizes,
sometimes it nearly hits the H and stays up there.  At these times, I've had
the oil temp run up to > 150 Celsius.  It doesn't stay for any particular
period of time, but eventually the gauge will drop back below 1/2, and soon
after the oil temp will return to 130 or so.  I would think that, at highway
speeds, the coolant should stabilize at some temperature.  Well, mine doesn't
stabilize even when running on cruise control on flat territory (Florida) for
any length of time.
I've tried removing the thermostat, but the problem still persisted.  I also
think that the car is burning/leaking oil far more than it used to, but I
haven't had time to check that out.  About a year ago I flushed the coolant
system and replace with Prestone Longlife, and the car has had lots of fresh
mix since then (like when the radiator hose blew).  I really have no idea what 
is wrong.

Please, any ideas?

Thanks,
Eric
gt6493c@prism.gatech.edu

P.S. My father's '82 Coupe is about to break 300K miles!