1. Tire pressure: Make sure that the tire pressure in all four tires is equal. If one tire is low, it can cause the truck to lean to one side.
2. Springs: The springs on your truck may be worn or damaged. If this is the case, they will not be able to support the weight of the truck evenly, and it will lean to one side.
3. Shocks: The shocks on your truck may be worn or damaged. If this is the case, they will not be able to control the movement of the suspension, and the truck will lean to one side.
4. Frame damage: The frame of your truck may be damaged. If this is the case, it will not be able to support the weight of the truck evenly, and it will lean to one side.
If you are not able to identify the cause of the problem yourself, you should take your truck to a mechanic for diagnosis and repair.