i'd try first checking for dust and things that could impede airflow. if you don't find any or what you clean out doesn't help, then i'd definitely try reapplying the thermal paste, especially if you are hitting mid 70s without overclocking.
well just did a retest of the temps after gaming for the last hour and cores are all at 64C the only one that concerns me is Aux was at 91C the rest all were pretty good