DRIVELINE & SUSPENSION KIT GRNExtreme Heavy Duty Upgrade Kit The Extreme Heavy Duty Upgrade Kit transforms your already tough Hoss 4X4, Rustler 4X4, or Slash 4X4 into the ultimate bashing machine. Engineered for extreme brushless power systems, the kit includes a full complement of driveline and suspension parts designed to work together as a complete package. Whether you're sending it at the skate park or preparing for a speed run, the Extreme Heavy Duty Upgrade Kit is battle