theres also an exhaust leak dye tester available thru dealerships to test for these overheat probs.
the prob may simply lie in your head gasket. not so simple actually. if exhaust gasses bypasses into ur water system,it contaminates and overheats it, eventually blowing the head and destroying ur water system as well. a new radiator may not cure the problem if ur headgasket is leaking. best bet is to test this with that dye tester...its yellow and should turn blue if exhaust gasses are present in ur radiator system. don't waste ur money on something if the problem doesn't lie there. try to isolate it first, then go from there. i got a feeling on this, i hope i'm right but at the same time hoping for you that its not.