Timm- I'm certainly no expert on M-B's, but I would check the radiator closely! My old fuel injected Land Cruiser consistently overheated, even after replacing the water pump, thermostat, hoses, everything except the radiator. It turned out the radiator was the villain. You might remove it and have it boiled out, or rodded out (whichever they do these days). I had mine rebuilt for $350 (!) but it no longer leaks and cools just fine. Also, as stated earlier by others, an engine running rich will tend to overheat. If nothing else seems to work, including the above, have you performed a compression check? Hopefully, you don't, and I wouldn't worry except as a last resort, but you might have either a bad head gasket or cracked head? The mileage on your car seems low, so it must have done a lot of sitting, that equals rust and corrosion and junk in the radiator and rest of the system. You have my sympathy; these issues are frustrating!
Just my $02. Good luck, Ned.