In the last few months I did a few things on my Ranger 4.0. I tried a tubular intake with 4" K&N on the end (inside engine compt.) There was a noticable improvement. I added a cat back Gibson exhaust, same thing, good improvement. Then I came across a deal, a Paxton kit and picked it up for $1,300. BIG improvement, same mileage(!) I towed 2 bikes + gear + etc. and got the same mileage as prior trips and it pulled up PA. mountains in 5th gear

I would say a good intake and exh should be worth probably 15-25 up top.