My brother is trying to trailer a 19' boat using a 1998 Plymouth Voyager
Minivan which supposedly has some sort of "towing package 2".

His trailer has hydraulic brakes....

When he towed the boat, he said the van was "bucking". Can a 6-cylinder,
3.3 liter minivan trailer a 2700 pound boat? Do you think the problem is
related to the minivan or is this likely something to do with the hydraulic
brakes on the trailer? Any thoughts?

Thanks