99 Pontiac Sunfire 2.2 Overheading Problem

Okay so I have a Pontiac Sunfire with the 2.2L that
keeps over heating weather I'm driving it on the
hwy or in city traffic. But I have replaced the
radiator, coolant reservoir and cap, upper and lower
radiator hoses, thermostat and thermostat
housing, water pump, and heater core and heater
core hoses. So when was replacing all that this
stuff I noticed that the coolant was a burnt orange-
light gray type of color and that all of the hoses
had a lot of corrosion bill up in them too, and the
old coolant reservoir had a dark brown almost
black billed up on the bottom of it too. And after all
of this 5 full coolant flushes useing straight water
to get all of the old coolant out of the engine, and
thin 5 more flushes with the right coolant for the
car it is still over heating and I just don't know what
to do to fix this anymore, cause this car is not like
anyother car. So can anyone point me to what the
real cause is or what I have over looked that would
be very appreciated