Strong shifting when changing loads in the VW T6 - especially when accelerating or decelerating in the 2,000-3,000 RPM range - can be caused by, among other things, a worn rear engine mount. In the image, the rear engine mount of a 110kW TDI T6, where the inner damping rubber was so worn that there was noticeable play when the load changed.
In the shown image of an 110kW TDI VW T6 engine mount (rear), the inner bearing of the mount is so worn that the metal core has almost completely lost its mobility within the rubber. This resulted in noticeable play of several millimeters, which was felt as a thud in the vehicle's floor when the load changed. Because excessive play in the rear engine mount also excessively loads the
front VW T6 engine mount, it makes sense to at least check it or replace it at the same time.
VAG part number for the rear engine bearing is 7E0 199 849 F.
The mounting can be relatively easily expanded if you loosen the front engine mount. Then the engine can be tilted forward as far as possible to remove the rear engine mount.
When replacing the engine bearing, no special tools are required. However, a longer torque wrench and 2 1/2-inch extensions, as well as a 1/2-inch swivel, are very helpful.
Note: The VW T6 is very similar to the VW T5, the statements also apply to the T5, excluding the VAG part number.