Is it possible to de-gloss paint

Probably both temperature and thinning are an issue, since you are at the extremes for both (very high temperature, and no thinning at all), but there are a LOT of ways to get orange peel, so eliminating it can be a trial and error process.

It sounds to me like the solvent is evaporating before the paint can flow together on the cabinets. This is usually a result of some combination of:

• low air pressure or fan adjusted too wide
• holding gun too far from the surface of the work
• temperature is too hot
• too little thinner

If your gun is adjusted properly and your technique is good, then I'd thin and try to work earlier in the day before it gets too hot. Mineral spirits would be preferable over naptha, because naptha evaporates more quickly.

When I use oil based products I use disposable pan liners so cleanup means let it dry-up and throw it away. To clean brushes I use a brush spinner to remove as much material as possible. I swish the brush in a container of mineral spirits and brush a piece of dry cardboard to get out some more of the urethane. Finally I soak the brush for a couple of days in a covered glass jar that has just enough mineral spirits to cover the bristles. After everything is clean I set the mineral spirits filled container in the sun uncovered until it evaporates. I would not dump it on the ground! If you cannot find a way to dispose of it contact your municipal public works dept. Most cities have an annual hazardous waste drop-off.