The OHV 4.0L is a great engine, it will last forever if taken care of and it shines in low end torque. It doesn't rev high so intake and exhaust are pretty much a waste for it. Your k&n intake is probably causing you to pull warmer air than the stock intake too.
I never looked but you could probably get a tuner/programmer to make some extra power with it. Some poeple like electric fans and under drive pulleys that reduce the parasitic load on the engine, but I liked the reliability without that stuff.
Honestly I think for long term reliability and usability in a truck, I would probably take the OHV version of the 4.0L over the SOHC they have now.
If you want something fast get a car.
2006 F150 FX4 Super Crew - Bilstien 5100s leveled 2", 35" KM2s, 4.56 gears, Detroit locker, Eaton E-Locker, Traction Bars, AEM intake, Xcal 2
2010 VW Golf TDI 6MT