highway yellow cat paint

If you had used a sealer under your Caterpillar yellow paint, and you had used the correct temperature of thinner for the air temperature, your paint would have flowed and glossed over. No sealer used allows the thinners to escape too soon to the primers and old paint below, thus leaving a flat finish. Using a colder thinner for a too warm of air temperature does the same thing. It evaporates too quickly before the paint has had a chance to gloss over. On my last coat of paint, I always add extra thinner so that the paint will flow for a longer time for that extra gloss. It is always better to put on extra thin coats of paint than to try to cover it all in two coats or less using thicker paint. Yellow paint doesn't cover very well so always expect to shoot extra coats for coverage when shooting yellow. If you use a low pressure/high volume paint gun, you will use half the paint to do the same job that a high pressure paint gun would use. The high pressure guns blow over half the paint away into the air.

Also keep in mind that that Cat paint is nothing but alkyd enamel, same as many common brands, is the cheapest paint produced and has been around since the 30's. It is more functional for rust and corrosion control than for show.

Another thing you may want to look at is moisture in the air lines. It will dull out the finish. I do not think the Cat paint was ever made to have high gloss as most implement paints do not.
Terry