Trany shifts all by itself
 

2001 town an country 3.8 197,000 my shifter has gone from drive to n to rev while in motion anyone no why or what would cause this

Try posting this up in the T&C forum. Be sure to specify which transmission you have. There are several members there from Britain and they often have manual transmissions.

Assuming yours is an automatic, first check the level and quality of the fluid. Hopefully it's been changed several times over the last 15 years but if not, it's waaaay overdue.

If that doesn't solve the problem, get it in to a competent transmission shop and have them look for error codes in the transmission computer. Go from there.