Simple..Underclock (or overclock) using GPU Clock Offset in Precision, as stated above..You can do that three different ways, and you need to click Apply after changing it..A negative (underclocked) value subtracts that amount from your card's specific Boost Clock Speed..A positive (overclocked) value adds that amount to your card's specific Boost Clock Speed.
1. You can move the slider by dragging it with your mouse.
2. You can move it by clicking on the slider button then use the keyboard left/right arrow keys.
3. You can change the offset by clicking on the number to clear it then typing in a number and pressing Enter..To lower the offset, hit the minus key before entering a number.
You should run the fan at 100% and see what the maximum GPU Temp gets up to..You can also create a custom fan speed curve in Precision..You might also think about replacing the thermal paste on the GPU chip..I see some of that has been suggested in your other posts.
To change the thermal paste (also simple), take out the four spring loaded screws on the back around the GPU chip to seperate the PCB from the fan/cooler assembly..Clean up the GPU chip and cooler plate with rubbing alcohol..Put a drop of thermal paste such as
MX-4 (or similar) in the center of the chip and reassemble..Do not overtighten the screws, very snug will do..Use not more than a BB sized drop of thermal paste, maybe even a little less..Don't forget to disconnect/reconnect the fan connector.
If you have not, you should enable the GPU Temperature alarm in Precision to warn you of running hot..Open the OSD Settings..Select "GPU Temperature" in the "GPU Statistic" dropdown..Set the "Maximum Value" to, say, 80C..Then enable "Play alarm sound when value is out of range"..Close the OSD Settings.