Make sure your brakes aren't dragging at all and that the drivetrain isn't binding.

Is the slipper clutch slipping? Is the ball diff jacked and slipping (not sure if Rustler has ball diff)? What kind of clutch/springs are you running?

That thing should be uncontrollable, you are right. What kind of controller do you have? Hopefully not the stocker. After 8 years I would hope that you graduated to a radio with end point adjustments and better response. When you open the throttle up, does the slide carb fully open? What kind of throttle servo do you have? Sometimes a faster transitioning servo (with a better radio) will give snappier response.