They say change / rebuild at 100K. I would think DOT might have done them. If you got records with it, judge from there.
Its not like a newer truck were it costs several thousand to change the injectors.
Glows, check them. If they all are good and AC's or Bosch's, then consider leaving them.
If one is burned out, or a goof ball brand, they are cheap enough to change them all.
Double check the wiring too.
Just an opinion of many.
Just like a hole s, they are all around.