Holden Rodeo diesel auto

I recently bought an 2005 of the above and i have a question. Hope i explain this right. Most autos ive driven when you take you foot of the accelerator the engine assists in braking. but i cant feel that braking in the rodeo. kinda odd as it has a real diesel 'chug' to it, take the foot of the juice and it all goes quiet. So does this sound normal?

i don't know what auto's you have driven but most auto's don't have much engine braking.
however there can be a couple of catches to that. a lot of auto's have a lock up clutch that engages typically at higher speeds (eg 80km/h). that can provide engine braking until the lock up clutch turns off.
also a lot of later model autos will down shift when going down hill to provide engine braking. but not all are designed for that.

all modern diesels turn off the fuel when going downhill. so the engine will go really quiet.

lets say the diesel does turn off the fuel down hill , so if it does do that it should engine brake . now what could cause it to not do this engine braking, one would be accelerator position is the potentiometer hall effect sensor reading o acceleration, but that dont tells the engine controller that you want to slow down. , there could be a tilt angle sensore so then it would know your on a down hill desend.
but there is one more sensor that every car has

The brake pedal position sensor . wrongly calibrated brake sensors or fault with it can lead to noumerous problem like cruis control not canceling automatic on some vehicles.

So that would need to be investigated and reading thru tsb manufacturer updates and possible flashes to remedy this problem as it could also be a knowen software issue-

Yes I would say that is normal, its a heavy vehicle, I have noticed this on the bigger Toyota diesel, you can button off and it goes quiet, as it should, the engine is idling, if you flick it out of overdrive it will make a slight difference, not much, it's all good.

I have little engine braking with my Terrano but when towing or on steep hills I remove overdrive and then engine braking is noticeable. Also switching on air cond on downhill run provides a small amount as compressor takes some engine power.