Not this again

[<Ehlem@domain.elided>]

Fellow Stag owners,

I know you've responded to a zillion or more questions about overheating, but
I've just got to ask again.

The Situation:

Complete rebuild on the engine. .20 over pistons installed. Everything is new:
hoses, water pump (six vane), etc. The valves line up dead on with #2 cylinder
at TDC. The radiator has been recored. The original fan shroud is in place.
The viscuous fan new and replaced (courtesy of Walter Holliday, Stag
Specialists). The coolant fresh. Filled with the heater in the hot position
and the front of the car jacked up to aid in the escape of air pockets. The
engine now has 3,000 miles on it. By in large it runs well with a troublesome
low end stumble that is more annoying than debillitating (sp?).

But it won't cool down!

I have an analog gauge in it which will read in farenheit 210 or more when
traveling 65 to 75 mph over any distance of 20 miles or more. This is a slow
creep up on the gauge.  The thermostat does kick in at 180 degrees because I
can see the needle steady (I have also done the boiling water test on the
thermostat). But after that point it is a slow climb up into the "oh my God is
it gonna blow" range. This temperature rise occurs in weather of 60 degrees as
well as 90 degrees. Finally, I have no coolant loss.

Thoughts that occur to me:

1. Is there a cavitation occuring over the water pump?
2. Does the 6 vane water pump simply not circulate enough water to cool down
the temperature?
3. Is it possible that I have incorrectly routed heater hoses? (okay, I'm
grasping here)
4. Is it because I have a BW35 and at 65 mph the engine and tranny have to
work too hard (33-35 on the tach) therefore creating excessive heat. (I doubt
this given that the problem will occur at lower speeds in high (90+) heat.

Tell me it's something simple that my less than agile mind didn't think of.

Regards,

Kim LeMasters
73 Stag