overheating

I have a 1985 Corolla that is overheating and I can't figure out why. My daughter owned the car and about 2 years ago she overheated the engine pretty bad and it's been sitting in her driveway ever since about Oct. of 99. It is a RWD with a 4A-C engine. I gave it a complete tune up, replaced the starter and battery (both were bad), and had the carb taken apart and cleaned, I would have had it rebuilt but couldn't find a kit at the time and had to get it running.
The engine ran good if it was in the driveway and above 1500 RPM. If I took it out on the road, it would immediatly overheat. I replaced the thermostat and the fan clutch and flushed the cooling system and it still overheated. I had it towed to the nearest Toyota dealer and was told that the head gasket was blown. I took the head off and had it straightened, checked for cracks, guides replaced and a valve job. I cleaned the water ports on the block and put the head back on, hopefully the head gasket is on right since it didn't specify which side was up, all of the holes lined up so I put everything back together.
Now, it doesn't overheat if i'm driving around town in the cold weather but once I get it on the freeway after about 10 minutes it will slowly overheat. I got it home yesterday and pulled out the thermostat and checked it in some boiling water and it opens at 190 deg. What haven't I done???????

uassaly whith toyota persistent overheating causese the radiators to become cloged with ressidue. were you getting white smoke from the rear of the car before the headgasket was blown?. and were you constantly adding water to the rad to top it off? if youwere then the radiator is definitly clogged you will probably need to have it replaced, it seems that there is so much build up inside of it that a simple flush wont do much.

another suggestion would be to ge the fuel mixture needle checked it may also seem that your running a bit lean wich will always cause over heating something to check for in this case is when your aout driving put the car in a low gear such a 4-5 or 2-3 if its an automatics and then floor it if you hear any knoking pining then you are might be running rich but just cause it did that doesnt meant hats the cause pining can also result from massive carbon build up in you cylenders do to cheap gas high miles and poor maintanece

hooe that givs you more to keep your hand busy

did you check the water lines when rebuilt the engine? including the water pump? have your rad checked too, it might need a serious cleaning (due to mineral deposits) to unclog it. next will be your aux fans.... are they working? hth.