Thanks for the follow-up ... great to know that it was radiator and not tstat ... this will likely help someone else as they troubleshoot their problems using this thread!
I have had overheating gremlins before and I though they were gonna drive me nuts ... it is probably a great relief for you to be able hammer it and then cruise in hot traffic with confidence!
BTW, one of the side effects I noticed after replacing my tstat was that it seemed to warm up faster than before ... have you had the same experience?
1991 350 SDL (200K and she ain't bent, yet)
former 2002 E320 4Matic Wagon - good car
former 1985 300 CD - great car
former 1981 300 TD - good car
former 1972 280 SEL - not so good car
a couple of those diesel Rabbits ...40-45 mpg