The first step would be to inspect the hoses going to and from the boom cylinders for any kinks or damage. If any of the hoses are found to be damaged, you will need to replace them in order to fix the drift issue. The next step would be to check the boom cylinder itself to make sure it is free of any blockages or debris. If there is debris in the cylinder, it will need to be cleaned out in order to ensure that it is functioning properly. Finally, you will want to check the hydraulic fluid levels to make sure that they are at the proper level and that the system is properly lubricated.