Viscous clutch test: Place rear chassis on rolling jacks, with rear wheels in the air. See if front wheels will pull van forward. If silicone shear fluid is low/gone van won't pull.
Put van in tight radius turn at about 3-5 MPH. Very slight binding is normal, heavy binding/hopping is indicative of bound up VC, usually heat warpage of the internal discs, which are packed close so the shear fluid works.
VC is one of the two expensive parts on the van, the other is the AWD transaxle so take care.
Matched, well rotated, properly aired tires are essential. If the tires aren't the same diameter, the difference in rotational speed churnes the VC, building excessive heat, which will destroy the VC.
Syncro has excellent center of gravity, Lots of drive train, way down low, plus lots of iron to protect the drive train. Conversion to a camper will change your center of gravity quite a bit. Transporter is a genuine one ton van, curb weight, ~4,000 Lbs.
Note on rough shifting: Each tranny oil behaves differently in this transaxle. Some are to viscous and the syncros won't work well, catches 2-3 or 3-4. 1 is not (Hehe...) Normally used, but handy. ;o)
http://groups.yahoo.com/search?query=syncroEnjoy!