I've been having the same issue but not as severe. When it gets hot or overheats does your fan get unusually loud with engine rev or acceleration then quiet down once it cools down or at higher speeds? Everything I've read I really think it's the fan clutch and am considering changing that. Have you found your fix

 

I am having the same issue as of This Tuesday. My D has been ultra reliable for such a long time and when I was running errands and got stuck in construction traffic it ran really hot. I turned the heat on as soon as the "Check Gauges" light came on. I am really interested to see how/if you fixed yours.

 

Clogged radiator certainly could be an issue. I don't know about oversized, but aluminum radiators certainly are better than copper.