Kiwikkiwik a quick search on YouTube will bring you many videos of modern military vehicles travelling at high speed off road.
The low-speed, low-gear careful driving you seem to be talking about is, as Imp points out, a civilian (less capable) vehicle driving so as not to scratch the body work - this is NOT how a military driver works especially not in a combat zone!
Example:
https://www.youtube.com/watch?v=A491rFrTvKg BTR (an older less capable vehicle...)