Which of the following should NOT be done to stabilize an upright truck?

Removing air from all tires is not a recommended practice for stabilizing an upright truck. This method may lead to unintended consequences, such as causing the vehicle to become unstable or facilitating a change in its center of gravity. Additionally, deflating the tires does not provide any structural support to prevent the vehicle from tipping or rolling, which is critical during rescue operations.

In contrast, adding cribbing under the vehicle, using stabilizing struts, and securing the wheels are all effective methods that increase the stability of a truck during rescue situations. Cribbing elevates and supports the vehicle, stabilizing it effectively. Stabilizing struts provide additional lateral support, preventing movement during extrication efforts. Securing the wheels helps to immobilize the vehicle, further reducing the risk of it rolling or shifting unexpectedly. Together, these methods create a safe environment for rescuers to perform their tasks.