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Do you still have the little green factory-issue covers on the bulbs that light up the gauges? If you do, you might try taking them off. Over the years they get clouded up and reduce the light output from the bulb. One of mine just fell off last year and the factory bulb puts out more than enough light for me to see the gauge face on the side it's on.
If you want colored light, you might try getting new slip-on covers for the bulbs (I think they're #192s....you might check before buying covers). Or you could try LEDs (available at stores like Pep Boys or online).
BTW, I have the LEDs for the Autometers on the instrument panel lighting circuit with everything else, and they do in fact dim somewhat. Not as well as incandescent bulbs, though.
#161 is the brightest incandecent that will fit without doing damage if you remove the colored filters from the cluster. They are hotter than #194 though, and will destroy the colored filters.
They also make Colored #194 bulbs. If you remove the old light filters out of the cluster, and replace them with Green colored bulbs, that is the closest match to the factory, and are as bright as when the truck was new. Industry #194-G They also make Red, amber and blue, if you prefere.
Also, if your light switch is worn out, or the rhetrostat that dims the dash lights on the switch is worn or dirty, corroded etc, that will cause dim dash lights too.