We've eliminated the mast as the problem. We have determined that it is a hydraulic problem, possibly in the return side of the hydraulic system somewhere in the control valve. Since the problem only occurs while the main lift cylinder is lowering, we determined it to be not the mast by taking another machine and using it's hydraulic system, and found the mast to be operating perfectly. So we have determined that there is a problem with the hydraulic system in this Toyota model. Ironically, there are two machines having the same problem, so we have determined that Toyota may have a problem with this particular model. Due to budget constraints, we were not allowed to take the hydraulic control valve and associated parts off for inspection. As the machine is operating fine otherwise, we returned the machine to the customer and put it back into service. Still, if anyone knows of any other problems with this particular model, note that this hydraulic problem will literally shake you off the seat of the forklift. Has anyone else had this problem with this particular model of Toyota? This is an electric forklift.