I see you have a pd engine unfortunate the newer cr engine is not happy in 5 th at lower speeds

No its even older ALH multipoint injection tractor. EGR delete, fast flow air filter panel.

from Estate Man: " fuel get completely cut off when you are off the throttle in gear " but when you drop below tickover speed ( engine ) it uses more fuel as it tries to regain revs.

It's all about anticipation and light acceleration.

Really wouldn't recommend slipstreaming for the small economy benefit it would bring. Generally people do it behind lorries, so forward vision is massively reduced as is the braking distance you would need to achieve in order to not crash. Quite dangerous IMO

from Estate Man: " fuel get completely cut off when you are off the throttle in gear " but when you drop below tickover speed ( engine ) it uses more fuel as it tries to regain revs.

Sure, of course. The fuel is only cut off when above tick over engine speed with the car in gear and moving with your foot off the throttle. If your revs fall to or below tickover speed at any time the fuel shut off valve opens up and the engine starts to fire again. In fact, the valve normally opens up supplying fuel again at tick over revs plus 5% revs on the majority of car engines wether petrol or diesel. This is to prevent stalling should you be about to stop.