Hi Paul,
Well, something IS fishy. (Iam not suggesting it is your fault....Grin)
I have the decoupler set to 1.48 and at 5mph, 3 cars went over it without uncoupling.
For some odd reason the Decouplers and the Retarders don't seem to work at all. I did it all by the books. It just doesn't want to decouple nor stop at the end of the tracks.