Model only runs for a few minutes (short run time)

Battery pack is not properly charged
Charge battery completely.
Motors are dirty or damaged
Give the motors a thorough cleaning and then install them back on the motor mounts.
Drivetrain is binding
Remove the motor's pinion gear and turn the props to check the drive train for binding.
Battery won't hold a good charge
Possibly the battery is damaged or your charger is not charging the battery completely. The battery should be slightly warm after the charge cycle.
Hot electronics
Let model cool down between runs.
Faulty ESC (electronic speed control)
Send the speed control into Traxxas for service.
Recommended reading
Re-oiling the bushing
Electronic Speed Control in Lipo-Mode
Determine if your ESC has LiPo mode. The default LiPo-Mode setting reduces power to the motor at a certain voltage. Stop and recharge your LiPo battery. If using NiMH batteries, you can turn off the low voltage detection for longer run times. Turn on the ESC, then hold down the set button for 10 seconds until the LED turns solid red. *Remember to turn back on Lipo-Mode if you use a Li-Po Battery at a later time!