Do you know what GPU you have? Different chips have slightly different specs, but I agree that anything over 85c is where I start to raise an eyebrow...unless it is a laptop. Those things will run as hot as possible anytime the GPU is doing much of anything! Regardless, 70-80c is unlikely to hurt anything.

The good news is that pretty much every GPU built in the last decade won’t intentionally kill its self with heat. If it does get too hot, it will cut speed and power draw to stay within acceptable limits.

Replacing the thermal paste can help, but shouldn’t be necessary to maintain safe temps. Also, while replacing the paste is easy enough, sometimes disassembling the card can rip or damage the thermal pads they put on other components, and when you replace those, you need to be more careful about getting the right size and type. Just blowing things out with a can of compressed air can often help, as can checking to make sure a fan hasn’t died. Not just the fans on the GPU, but a dead case fan can also cause trouble.

- Bret