I should of said open air intake but they must help by allowing more air in then stock or is stock air box with a K&N drop in filter as good?
The one I was using before I returned to stock for emissions testing seemed to help at highway speeds. Was easier to accelerate uphill in 5th and hold 80-85mph.
But, your low end seems to suffer a bit. Probably too much airflow and not enough fuel flow at low speed and your MAP sensor reads low pressure; low speed also leaves it taking in hot air which probably causes the ECU to retard the timing, also.
Return to stock airbox and paper-filter and you seem to have (a little) more low end torque, but then your high-end suffers some. For off road, you don't really need the high-end though unless you are trying to break something
Going to try the open filter/pre-filter route again with this IAT mod I bought and see if added fuel flow makes the open filter setup all-round better (until emissions test time, that is)