Basically, Disco gear ratios are pathetic.
For serious work, first is too high, second is far too much higher than first, and so on. The gear spacings are like ordinary cars, which landies are not.
Most cars are set up more or less to the following plan
at 1,000 rpm of the engine, road speeds are:
1st gear - 5 mph
2nd gear - 10 mph
3rd gear - 15 mph
4th gear - 20 mph
5th gear - 25 mph.
This means in a TD5 Landie with a big trailer on the back, you need to hoick the engine revs way up far too high in first before you change into second, at least up to 3,500 or 4,000 or the gutless bugger will die on you when you shift into second. Grrr.....
Synchromesh in the transfer box would be good, or an epicyclic change from HI to LO.
I liked trucks with fifteen gears - one suitable for every occasion.
CharlesY