This is a question best asked at a salvage yard. They have huge, very expensive "Hollander Guides" that list every part for every year and model, with a code number. You look that number up in the back of the book, and it will list every application that used that part. The people there will also know if you need the flex plate or torque converter that matches the year of the van or the year of the transmission.
You have the wrong engine size listed. For the '99 model, there were two different engines available, and they call for different transmission part numbers. The 2003 model calls for yet another part number. The problem is we don't know why those numbers are different. The differences could have no bearing on one transmission working in a different application. Some possibilities include one might have an additional sensor, and the other one doesn't have a place to put that sensor. One could simply have an extra ear cast into the housing to mount something to, and that wasn't used or needed for the other year, so it was left off.
I suspect the difference you're going to find will be related to electrical things, including sensors and controls. There are a real lot of changes taking place just from one year to the next, and you're looking at four years difference.
Monday, May 1st, 2017 AT 4:51 PM