Temp rises on gauge when you speed up.

[curbill]

On my 1980 300sd at 45 mph the temp gauge maintains 93 to 95 degrees. As you speed up to a steady 55 mph the temp gauge goes to 100 degrees. It maintains the temp as you drive. If you drop down to 45 the temp drops.
The engine has a recored radiator. New water pump, new auxiliary water pump, new 80 degree thermostat and new hoses. The engine was flushed and new antifreeze has been installed. All of this within the last 200 miles. The auxillary water pump has ceased to function within the last 2 days along with the a/c which has also been repaired with in the same time period.
I am stymied as to what is happening. On my 300 wago if you got into traffic the temp would go up as the speed decreased. When the pseed increased the temp would drop. This is opposite to what we are experiencing with the SD. The fan belts were also replaced. Any suggestions