Thank you for the advice. The unit is used in a warehouse, so the mast channels are clear. The cap on the lift cylinder in the middle of the mast was replaced recently, so I did bleed that cylinder. I returned it to them and requested that when used they pay attention to when it was bouncing, specifically where was the carriage when it was acting up, on the center cylinder or the two outer cylinders, or after they stop lowering. I am waiting on more information.