1990 302 Bronco Tune-up

I have been noticing that my gas mileage isn't as good as it should be lately, is there anything else besides a standard tune-up that I should have checked over or done that can make sure everything is working a ok? Thanks

Always start with the airfilter if the engine consumes abnormally.

i have had a k'n air filter for the past 10,000 miles

have you checked for DTCs yet?
checked plug cables for leakage when firing? (at night, no lights, look for spark leakage along wire path esp on pass side under egr valve where they run clost to the valve and stuff
pulled some plugs to ck gap and condition?
pcv valve changed in last 60k miles?
other checks can be done at more cost & diff.; egr passage in intake man. cleaned in past 60k miles?
vacuum gauge readings?
and so on