I can't speak for the Pacifica, but the T&C says to tow in drive unless the shifting is irritating and then use the manual select option to pick the gear especially going down grade for engine breaking.
The T&C was more than adequate through the mountains around Yellowstone and Glacier National Park etc, but there is no comparison with the Touareg.
Where the T&C would downshift and rev to 5000 rpm the Touareg rarely had to downshift more than 1 gear and never to more than 3000 rpm.
The most irritating thing was that you could limit the highest gear, but not the lower gear.
But the T&C towed safely and competently all over some terrain that has "Big Rigs" crawling and never showed a sigh of running hot or any other distress.
That was with our "Heavy" 16' Scamp
(28-900 lbs + gear)