So I recently started tuning up my 90 5.0
So far I got plugs, wires, cap, rotor, timing adjustment, air filter, fuel filter, tires, oil change, and alignment.
I'm currently getting around 15 mpg highway. Anything else I should replace, change? Thanks!

You said you've gotten tires. Double check your pressures and adjust accordingly per your wants. Fuel mileage usually equals max pressure, while ride most of the time will be considerably lower pressures. If it's mpg's your looking for, you can look at bumping the timing to around 15 to 16 degrees. Power and mpg wise you can look at an electric fan setup. E Fans give the biggest bang for the buck IMO. You can almost guarantee another 2mpg with the fans and spend less than $50 if you have a good salvage yard around.

https://www.f150forum.com/f10/electr...ght=e-fan+swap

https://www.f150forum.com/f10/just-g...ht=gained+8mpg

Don't forget the tranny! Change the fluid and filter. Also drain the torque converter, just dropping the pan only gets part of it out.

If you're feeling adventurous, suck some seafoam into the engine and let it sit for a bit. Then start it up and blow it all out!

Maybe a free-er flowing exhaust if you'd like to help it breathe out better. I cut open my old exhaust after replacing it, and man... I'd instantly replace that muffler on any OBS truck after seeing the stock unit's flow pattern. Ew.
It doesnt have to be anything loud, there are plenty of quiet mufflers out there...

If you have a vacuum tester, go wild under the hood and make sure all your vacuum lines and equipment are in check. The white plastic line right underneath the hood-hinge on the passenger side, tends to crumble.

Ign Coil, Serp belt, idler and tension pulley.

I have a pretty simple exhaust... Just a cat and glass pack... Just goes straight back, hops over the rear diff and exists out the back. Minimal turns. And I don't have a vaccine tester. Also I do run sea foam every now and again (half vacuum line, half gas tank)