First the gear selector with the Ford 5 speed has D, 3, 2, 1. Note there is no "4".
No the tow haul does NOT take you out of 5th into 4th. The tow haul changes the shift points to a little higher RPM's. It also will force a down shift when going down hill to take advantage of engine braking. It also locks up the torque converter under some conditions that the normal shifting doesn't.
There are not a lot of makes and models for Ford chassis for RV's. There is the E-350, E-450 and F53. (Yes there are a few RV's built on the F-450 and F-550, and I have seen reference to a F59, but they are not part of this discussion) I don't believe Ford has made changes in the gear shift selection in the 5 speed on the chassis models since they introduced the 5 speed and added the tow/haul mode.