It could be your radiator. I had a similar problem with my EG. My car had erratic overheating problems. Not coolant-exploding, detonating catastropies, but more in the area of my temp guage taking a trip to the moon once and a while. I changed everything - new hoses, thermostat, fan, fan switch, new coolant - I even had the radiator (a brass/copper OE replacement, on the car when i bought it) tested, and repainted.
Well, turns out the shop that "tested" my radiator was t3h suck, and according to a local shop (which I trust a good deal), the brass/copper rad's rot to hell in NE winters. I took my car to his shop, and after yanking the radiator, he told me that half the core was rotted, and that I was lucky it hadn't sprung a leak. The corrosion basically cut the cooling capacity in half, and thusly, caused my overheating problem.
In all truth dude, I can guarentee it's your radiator, or possibly your cap.
Hope it works out.