While manual trucks and SUVs are becoming harder to find, they still offer some advantages over the more popular automatics off road. These rally race school instructors take an auto and a stick shift out on the same trail to demonstrate the differences.
Some modern automatics have electronic descent control, but for older trucks that don't have that feature, shifting into a lower gear in a manual transmission still provides a smoother, most controlled descent vs the automatic.
The manual also has an advantage climbing, where selecting your own gear means a more predictable experience than the automatic that sometimes will shift up or down when you don't want it to.
Where the automatic shines, though, is on slower, more technical sections. Being able to crawl along at low speeds without worrying about riding the clutch or stalling the engine is much easier than the dance it takes to balance throttle, clutch, and brake at low speeds when you have to row-your-own.
Overall, which transmission is best will depend on your preference and type of off roading you do.
Related: Can the Jeep Grand Cherokee SRT go offroad?