When you intend to use 5th gear you need to tune the engine...
Ours cruises happily in 5th on Motorways and fast A roads. Not sure which model year you refer to, but the axle ratio changed on 4/4's in the last 4 years.
Paul Costock, UK 2014 4/4 Rolls Royce Garnet Red Disco 5 Teddy - 17h1 Irish Draught cross