If your engine is running fine throughout the temperature range, from cold to hot I would assume your temp sensor is fine. Check and doublecheck all connectors for oxidation, check that relay connectors are in correct position. Check that the ecu connector is attached properly.
Have you checked that you have 12V present at the relay socket with engine running? There should be 12V at pin 2 and 3.
Does the fan run if you bypass the relay? Short the pins 3 and 5 in the relay socket. If the power side of the fan circuit is ok, you should be able to get the fan running when engine is running. If not, this where you should focus your efforts. Relay pinout can be found in the '05 user manual.
If fan runs by jumping relay, there is a problem in the relay activation part. Remove tank, diconnect ecu connector and measure the connectivity from relay socket pin 1 to ecu connector pin 5. If that checks out you need an ecu diagnostic pc/software to diagnose the ecu.
I measured the cold resistance of my temp sensor, at approximatley 5 deg Centigrade, the sensor measured 6.9 kOhm. Heating the brass hex nut with my finger for a minute, the reading was now 6.75 kOhm.
Happy hunting.