ok, follow up, 02 trep 3.5L police were 104k miles: it appears the problem, this time, is the t-stat. I've literally owned hundreds of Mopars, and I have never had a working t-stat die on me. I've bought defective aftermarket t-stats, but I've never had one just stop working for no apparent reason, certainly not a Mopar oem one. I bought a new one, and tested both new and old on the stove, and sure as hell, the old one would not open. I replaced the water pump(the impeller had not slipped as I had expected), because I had bought a new one anyway, and upon closer inspection I found that there was evidence of some leakage at the weep hole.