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<635> Running Hot

My '85 635 is running hotter than it has in past summers.  When sitting,
idling in traffic the temperature gauge will climb up to the 3/4 mark, not
all the way to the red but higher than in previous summers.  It also seems
slow to cool down even when I get to traveling freeway speeds.  It is hot
here in Dallas and that may be part of the reason, but even at 60+ mph it
does not seem to cool down very quickly.  I've always thought cooling
problems were pretty simple until now, but I am still having this problem after:

        Replacing the reservoir tank-it had been weeping a small amount of
fluid from a crack
        Replacing the pressure cap-it was old
        Replacing the fan clutch-it would spin freely even when hot
        Taking off the radiator and having it "rodded out" by a local shop
        Replacing the upper and lower hoses (while the radiator was out, may
as well)
        Changing all the belts and making sure they were tight (same thinking)
        Replacing the thermostat
        Making sure any air was bled out of the system.  
        Checking to see that the auxiliary electric fan comes on when AC is on

There is not much left to replace except the water pump and I am reluctant
to tackle that without any better indication that it is the problem.  This
leads to my question: Has anyone had a water pump begin to fail without
starting to leak at the same time?  I am out of any other ideas.    Can I
trust the temp gauge?  (I am a little leery of it since if I watch it
closely, I can see the needle waver in time to the turn signal)  Is there
any way to test it other than buying a new gauge?  Any thoughts would be
appreciated.

Bob Hannesschlager
1985 635
BMWCCA #94537