My brothers got an '03 grand caravan with 75k on it. it has a clunking sound in the auto. tran. when you slow down, I'm thinking it is going from 4th to 3rd or 3rd to 2nd. I've not seen the van he called to see if I could help. I'm just visiting this group I'm normally on the Dakota group.
Heard it could be the TCM. I told him to flush and fill and go to dealer to check TCM.

 

Tranny oil cooler might be clogged....Flush it too but its a good start to flush n look for codes in TCM

TSB on this.....Involves reprogramming TCM on certain models