So I took Troopersphere's suggestion and pulled the radiator to give it a
gardenhose flush. Plenty of flow through it. Aside from the sixteen years of bugs and flotsom embedded in the front of the radiator it was pretty clean. Then I encountered a supreme Homer moment... the
"Doh!" kind. I checked the belts while I had the radiator out. Aside from the fact they were hard, shiny and glazed I had an 1" of deflection on the belt that turns the water pump and alternator. Well, no wonder it was overheating! With that belt I'm suprised the water pump turned at all. Much as I try to complicate things they always turn on the simple stuff.

And I decided to change the throttle stop while I was at it to increase the idle and adjust the TPS to accommodate the new position. Someday some one is going to have to make a tool to loosen the lower screw on that TPS. I futzed for an hour trying to angle in a phillips tip in a little box wrench then gave up, took off the EGR, took off the 19mm bolt behind it and angled a skinny flat tip screwdriver through the bolt hole of the EGR to catch that lower screw. What a pain.

Anyway, as predicted no ill effect. The idle with the stop adjusted has returned to "normal" (at least I can stop without keeping half my foot on the gas pedal), and the overheating is a thing of the past. Thanks all for really helpful tips.

And a week later I still haven't lost any coolant so it would appear the rings are my gremlin.