I have a 2006 Ford Ranger sport that has a missfire and the plugs, wires, and fuel filter has been changed. Still has a misfire, what else could it be?

P0301 is a engine misfire code for #1 cylinder , spark plug or plug wire problem or a bad fuel injector . Po171 system lean code . Lack of fuel , clogged fuel filter , vacuum leak . https://www.obd-codes.com/p0171 There are ways to test O2sensors before replacing . Your best bet take your vehicle to a qualified repair shop .

Since yours has ignition wires, it has the DIS coil option (as opposed to individual COP coils on each plug). The Coils are famous for failing, and the module is built into the coil pack. If you have the OBD2 fault code, it should have told you if there was a coil primary fault and/or which cylinder(s) are misfiring.
Checking for 26kv minimum spark at the affected coil tower is the next step. If you dont have a spark tester, either HEI style (fixed 30kv) or adjustable...this test is difficult. But since at least some cylinders run, the coil pack is a likely suspect. Injectors or compression may also be at fault, but are much less common failures on that vehicle.

check or replace pcv valve. check the hose also. remove and clean the idle air control with carb cleaner ( IAC ). they are usually located on or around the throttle body. check all hoses for a vacuum leak. good-day!

How often does it misfire? A slip in a timing belt/chain can cause missfires. Bad spark plugs as well.

MISFIRE ON CYLINDER 2 COULD BE LEAKING INTAKE AT CYLINDER 2 OR DIRTY CLOGGED FUEL INJECTOR AT 2 CYLINDER.REPLACE AIR FILTER IF IT LOOKS DIRTY AND CLOGGED UP AND CHECK TRANSMISSION FLUID LEVEL.IF FLUID LOOKS BURNT SMELLY CHANGE FLUID AND FILTER.

most likely the coil or ignition module

Try replacing the fuel filter then remove and clean the EGR valve also check the purge canister valve to see if it is operating correctly. and if all else fails rent a fuel pump tester from auto-zone or Schucks and test fuel rail pressure.

You might have a coil pack causing this. You need to see if there are any codes in PCM to see what cylinder is causing misfire and if there are any other codes. You can have codes with no engine lamp on.

Take your time, if its been awhile do a complete tune-up. and preliminary check a misfire can come from a defective cap and rotor, fuel and air filter. a leak in the fuel system or defective regulator.

No the only thing the san would show is a missfire, you need to test the injector and make sure it is getting fuel to the cylinder