4X4 Extreme Heavy Duty Upgrade Kit. Extreme Heavy Duty Upgrade Kit (9080)The Extreme Heavy Duty Upgrade Kit transforms your already-tough Stampede® 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-hardened to withstand brutal punishment and come back for more. Xtreme Upgrade Kit Features. Maxx®Duty driveshafts with 6mm stub axles. Heavy duty caster blocks, steering blocks, hub carriers, and shock towers. Fully compatible with HD suspension arms. May not work with sway bars or other accessories. Accessory part for these models. Ford® F-150® Raptor RT 4X4.