Careful with a D2 transfer box without a tune if fuel economy is your goal. I have found the opposite with consumption going up. It seems the vehicle has to work that much harder to achieve the same speed, even if the revs are lower.
I used to be able to get 480-500miles out of my 110 tank consistently with motorway driving, now its a lot more like 390-420.
However, for me, the drivability and quieter motorway driving outweighs the fuel penalty. I would imagine a tuned engine would 'pull' the box better, but that might be open to debate. Next on my list, would have done it a long time ago if it didn't ramp up insurance premiums so much !
A stage one remap shouldn’t affect your insurance premium (“engine chip 10-25%”)
And it makes a big difference to the Defender with no downsides at all.
Try Dynachip. He will come out to you and he charges about £250
I find that l don’t need to change gear so much and it climbs hills in fifth that previously needed fourth.
I would imagine you’d get even more benefit when a Discovery transfer box is fitted.