So...the powertune setting effects the same thing as power limit? Are you sure? If so, I need to edit my config file.
Oddly, I have powertune 30 set, yet it still bounces until I set power limit in afterburner.
Not 100% sure, but I had this problem, and played with those settings a lot. One thing I also learned... reboot when you change settings because old settings will stick and mess with your experiment. For example, if you set powertune to 20 and run for a while. Then you remove the powertune command all together, the old 20 value sticks...
But also I've never run at 30? I thought 20 was the max safe value.