Below are some threads from the now-defunct “Toyota Van People” forum dredged from Google's cache. This is by no means all of the great information that was once there, but what I could find a week or so after the site winked off. This is almost all from the Previa Tech forum, too.
TVP is apparently gone, but will soon be replaced by Toyota Van Tech
A discussion of SADS rebuilding options
A view inside a Previa automatic transmission
Throttle Position Sensor (TPS)
Previa Special Service Tool source
Typical Previa issues to be aware of
Previa heater blower motor/switch issues
Battery terminal issues to watch for
Collision catalog – part numbers galore
Tim's tricky heater core replacement procedure