You are on the right track.

A217 adx file will give you all the engine data for your van if connected to a 4L60E transmission.
A218 adx file gives you all the 4L60E transmission data. There are two different messages, hence the Trans1 and Trans 2.

You will want to download all three adx files. Switch between them to see what info they have. If you are concerned with your transmission, I would look at Trans1 first. Trans1 has 60'ish bytes of information where Trans2 only has 30'ish bytes. Trans2 primarily reports the adaptive pressure modifiers.

If you had a manual transmission you would only concern yourself with the A217 adx file.