At this time, the only truck I am aware of that locks the front and rear differentials is the Daihatsu Climber. No other brand locks front and rear. The Honda Acty Attack!, Suzuki DiffLock, and certain Daihatsus have rear locking Diffs.
You might be right on that. Other info I have come across: On the Honda Attack it also gives you a ultra low reverse as well as regular reverse and ultra low first.
Subaru Sambar had rear diff lock as option as well, I have pictures to prove it.
'91 Subaru Sambar SC KS4 c/w Diff Lock
Dyno'd at 69 HP@ Rear Wheels 61.5 ft/lbs torque