as most of you know we have been in the process of a complete rebuild. well today we finally got everything back together and fired her up and she turned over on the first try and ran like a dream. oil psi started high but then leveled out around 25psi (good) vac at idle is around 10 i believe it should be around 18-20 so i might have a vac leak but under load vac drops to 20+. Motor smoked at first most of which was the copper gasket spray on the manifold and the assembly lube burning its self off. made sure we filled the coolant up (a little more than a fill jug of coolant and topped oil off right. There are no leaks what so ever. Car does not smoke now and idles perfectly at about 800rpms.
Now on to the problem:
the motor still overheats. The old motor had 120,000 on it and it only overheated while under a load at about 55+mph while idling however it never overheated.
Now the car reaches operating temp and instead of it staying there it continues to climb until it finally overheats (coolant actually boils and fills the overflow tank up till it pours all over the place)
with the old motor we replaced the sensors (both), the coolant lines, the water pump, the thermostat, and the rad cap. With the new motor all that is mentioned above is new and we bypassed the heater core.
i really don't know what is causing this car to overheat as we have replaced everything it could possibly be with the exception of the rad itself which we will be replacing tomorrow however both hoses are getting hot and water is definitely flowing through the motor its just not cooling off??? and yes both fans are blowing hard as hell on the rad while its overheating.

I guess the point of this is to see if there is possibly something anything i can be overlooking here or is this car just doomed to overheat for no reason at all? There's a ton of experience on here with these kinds of issues so I'm looking for replies from someone who can possible solve this mystery for me. I'm at my wits ends it just makes no sense? if i replace the rad and it still overheats there's no where left to go? sorry so long but i wanted to make sure the history was explained and most questions were answered so that replies can be helpful.
thanks in advance
Joe

Stock Radiator I take it?

Yes

Replaced rad with another one and seemed to fix the issue however the car still runs a little past half way. atleast it doesnt overheat. Mine is always half way never goes any higher. so even though both hoses on the rad were hot it still had something wrong with it because the old rad caused the car to overheat all the time

now that you've got a radiator that can handle the cooling, get a proper temp gauge. the factory gauge is a glorified warning light that tells you when the car is cold, normal or toast.