soo...

you've bled all of the bleeder points shown in FSM?
changed thermostat...waterpump etc..?
water wetter ftw!
my friend with a FC rx7 had a problem with the belt being too stretchy/loose
so replace that..
radiator cap have anything to do with cooling? idk about it opening up to the overflow thingy
oh yeah..flushing everything out eh?

just making a checklist..hope it helps out
i tilted up my hood old-school style..hahaha..i am pretty sure it creates a small vacuum to suck out some of the hot air in the engine bay during highway driving...but that's just what i think