What would cause a 1995 ford Windstar to jerk into gear when stopped or slowed down?

It's the Torque Converter. Some symptoms also include a surge when you place the Van into Drive. Usually when the Torque Converter goes, so does the transmission since it causes internal damage. You will need to decide if you want to have a shop fix the Torque converter, have it overhauled or get a new transmission. Check prices with your local Transmission shop and call Ford about a new transmission. A new Ford Transmission will cost you under $1900 and you will get a better warranty then you'll find at AAMCO and Cottman. Sometimes it will cost you in excess of $2500 for shops like AAMCO and Cottman to rebuild your transmission and even in my case, it wasn't done right the first time. To avoid Transmission problems on Ford Windstars, install a transmission cooler. It ties in on the lower return line entering the transmission on Driver's side. Very easy to install, and cost = $80. The transmission is poorly cooled, and will fail...