Page 37 of the manual under "TRANSMISSION TUNING" or type in "Jato Slipper Clutch Adjustment" in the seach engine on the main page of the Traxxas web page.
Nitro Rustler™, Nitro Stampede™, and other two-wheel drive nitro models: To check the adjustment, hold the model so that the driving wheels cannot turn. With the drive wheels locked, push on the spur gear with your thumb. It should be difficult, but not impossible to move the spur gear. If the spur gear moves easily, then tighten the adjusting nut and retest.