One point is EGR.. The little devil EGR usually ruins engine braking.
Most manual transmission cars in my recent past have needed to block the EGR valve in order to get ANY engine braking..
I wonder if the Mk3 setup is shutting the EGR so there really IS some engine braking.
In my manual 2012 if I am using cruise control on a long downhill (Here we have a long hill going up to the local water divide on I94 from Milw to Waukesha) with cruise on.. the car does maintain the speed limit.
In neutral on the same downhill the car gains over ten mph.