It might feel slower because off road mode does a few things including changing the ratio that the throttle body opens up according to your foot. Its a linear taper in off road mode. Ford does it to help take off in sand so you don't just dig and for overall controllability. It also widens your shift points, so the transmission holds in gear longer, this is so if you need to let off the throttle for a corner or whatever the truck wont up shift. This way the truck doesn't need to downshift to get back into the power. The off road mode also desensitizes the air bags and changes the ABS system to better stop on dirt.
With that said I think off road mode sucks, I hardly ever use it. The linear throttle tapper holds the truck back imo. You can produce the same throttle control with practice by feathering the throttle when needed. The transmission shifting is better but its way easier to just manually shift the truck yourself. I've never been able to feel the better braking in off road mode, it stops damn good without off road mode. As for the air bags, I'm not worried.
When I'm gettin after it I shift into 4x4 or lock the rear diff depending on what terrain I'm in, hold the TC button down for ten seconds, drop the shifter in 1st and give her hell.
The down hill descend control is worthless too.