4X4 trucks sit higher........nature of the beast.
If you go measure other brand 350/3500 4X think you will find similar heights.
Already have a FW....then measure with it sitting level.
Between hitch and pin box adjustments most can be set up with proper bedrail clearance.
Some FWs have height adjustments via mounting holes in sprig shackles.
Some may need 'axle flip'
Some may need mods.....such as square tubing/cross bracing added.
Also there is an 'alignment kit' that adds roughly 2" in height.
A properly set up truck/5th wheel is a pleasure to tow.