Some Dodge vans were notorious for handling problems. If it has single tires in the back check and see if has had wheel spacers put on the back. The older Dodges were a few inches narrow in the back than the front, and the spacers helped them track better. Some just couldn't be fixed.
I suggest you read the faq's at the top of the Class B home page.
Lots of info in the archives. This will get you started about wheel spacers.
http://www.rv.net/forum/index.cfm/fuseaction/search/parms/sw%7Bwheel%20spacers%7D%7Ckm%7Bexact%7D%7Ckl%7Bm%7D%7Cfm%7B21%7D%7Cpd%7B366%7D%7Cma%7B%7D/sr/1.cfm