Looks like 3.4V is max for lipo threshold and I guess this ESC reduces power by 50% for a couple seconds when hitting LVC...but then it supposed to shut down I believe? I dont think its supposed to work periodically? I didnt see it but is the ESC supposed to flash red when LVC is hit? Or is trhat something else?

But I would NOT reduce it to 3.0V LVC....just for safety sake. You shouldn't have to and really, you should get decent runtime with a 5000Mah 2S lipo without resorting to lowering your LVC.
Are you sure you're charging your lipo fully to 4.2V per cell? And your ESC is not getting hot? Because thats one of the safety precautions they built into that speed control as well.

I dunno, I would re-calibrate the ESC to your transmitter, check all your settings for the ESC, charge your lipo up FULLY and try again. And of course make sure your Rustler is GTG (pinion/spur mesh, wheel bearings, etc.)