If the mixture is lean across the whole range, then you have a weak fuel pump, plugged filter, or a fuel pressure regulator that is out of whack. Set fuel pressure at 31 psi and see what happens.

The mixture adjustment screw on the ECU ONLY changes the mixture at idle.
You need to mess with the apparent resistance of the engine temp sensor to
change the mixture under power. You could put a 2500 ohm pot in series with
it and gradually increase the resistance until the ECU thinks it is cold and
richens the mixture appropriately.
--
George Downs, Bartlesville, Oklahoma, Central US

Are you aware that K&N filters trap very little of the grit going into your engine? There are some good articles on the web about racers who have run K&N filters and performed engine leak down rates (indicating piston ring wear) before and after races using K&N versus paper air filters. The K&Ns are just marginally better than running no air filters.

Overly lean mixture or hot combustion temperatures may be caused by not enough fuel pressure, clogged passages in the throttle body (if you have one - maybe yours is mechanical?), clogged fuel filter, weak pump, timing out of adjustment, incorrect spark plugs (too hot), bad thermostat or water pump causing high coolant temps, etc. Make sure to fix the simplest (cheapest) things first,