What is critical to ensure before traveling uphill with a load?

To ensure safety when traveling uphill with a load using a telehandler, it is crucial that the load is balanced. A balanced load minimizes the risk of tipping over by lowering the center of gravity and improving stability. When traveling uphill, the incline can increase the likelihood of instability, making proper load balance even more essential. If the load is not balanced, it could shift during the ascent, causing the telehandler to become unstable and potentially roll over.

While the other options address important safety practices, they are not as directly related to the primary concern of safely traveling uphill with a load. Lowering the boom can help with stability, but it is not as critical as ensuring the load is balanced before beginning the ascent. Similarly, having all personnel clear is always important for safety, but it does not directly impact the telehandler's performance on an incline as much as load balance does.