is there a way to run my 5970 stable?
90 is to hot.
You should use software that can control the GPU fan speed and crank it up to max, and put big fans blowing on the cards.
Old-skool mining pic of what is appropriate:
Also, 5970s are power hogs, the max power rating at stock is 290 watts per card, your power supply might not be able to keep up.