Question about my scout overheating!

[XxFWMxx@domain.elided]

Ok about a month ago my scout started overheating all the time, so I got a new
stant thermostat and put it in.  After that is was fine for about 3 weeks. Now
that it has gotten cold it is doing it again, it gets hot really fast and
stays in the middle of the temp guage.  When it gets really hot like that it
looses all of its power.  Does anyone know what the problem could be?  Should
I replace the thermostat again? Is it something in the radiator?  What?
Thanks,
   Matt Cason