Not alot of after market parts for that engine, super charger is about it, and not a cheap option.
Google: Ranger throttle cable mod
You may not have full throttle now, surprising how many don't and never noticed
4.0l OHV has 160HP but Ranger 4x4 weighs 3,500lbs, so not a light weight to push around, lol.
People also put oversize tires on 4x4s, this lowers the rear differentials ratio
so if you have the common 3.73 ratio and put on 31" tires then that ratio drops to 3.50 or so, which is great for MPG on the highway but makes low end power go away
So with bigger tires you should think about 4.10 or 4.56 ratio swap, have to do BOTH front and rear differentials