What caused you to do all the work initially? Where does the temp run when it is working correctly? What was the "failure mode" ... did it just "happen" one day or did it get slowly worse?
Does it overheat while constant state 60 mph on flat road? If not, and it only overheats after you come to a stop, it could be viscous-clutch fan (don't know if you have one of these or if you have a magnetic clutch fan) ... unless your temps are real high, you may not even get to the temp (around 105C or so) that will kick on the electric fan ... could be a bad tstat (sometimes happens) ... was it mounted correctly (they have been put in upside down ... on the other hand, I don't know if it would run without overheating in this case even on the road at 60 mph level) ...
You are in luck, though ... there have been many overheating stories this year with lots of good information being passed on the various overheating threads.
Worst case is that it is not a cooling issue, but a head gasket issue.
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