Why does my old, beat up car have a misfire?

I have a 1996 Mercury Sable with 260,000 miles. It has a misfire that occurs at about 2k rpm–not below or above while on level road, going up hills, and while idling when the engine is warm, say, at a stoplight after I’ve gotten off the freeway.

There are no obvious vacuum leaks, the fuel filter is new and pressure is fine. The plug wires are fresh, but I’m not sure about the plugs themselves. Thoughts?

Not sure about the plugs? Pull them out and take a look.

I plan on it. The top of the intake manifold covers half of them though, so it’s a Saturday afternoon just to take a look.

Also do a compression test. With the age and miles, maybe one of the cylinders is getting weak. A weak cylinder may mimic a miss.