Malayan box turtle breathing

Question
Hello, I'm a bit concerned about my Malayan box turtle. He changes his breathing behaviour if I take him outside. Normally he stays in a heated vivarium, with a UV light. They have woodchip substrate/slate (50/50), a water bowl, and I spray to keep it humid. I take them outside for short periods of time if it's warm enough. However, soon after they get outside this particular turtle starts gaping, does sharp intakes of breath and seems to have more saliva. Could it be stress? He's been treated for respiratory problems in the past but has been a lot better since I increased the temperature in their tank.
Another thing is he seems to get fixated on particular foods. He's typically very lively and alert and doesn't normally blow bubbles (He spends the entire time outside rushing around the garden!) Many thanks.

Answer
Hello,

What temperature gradient do you have in the vivarium? Have you ever seen this behavior in the vivarium? Have the others ever shown any signs? Where are you situated geographically? What diet do they receive? Any supplementation?

Terrapene sp. / Cuora sp. / Amboina sp. generally will need good ventilation but with high enough temperatures and humidity which may prove challenging.

What has he been treated for in the past?
There are many pathogens that may affect the respiratory tract including viruses and bacteria especially. Mycoplasma is a common isolated pathogen and although may be readily treated, it may prove problematic and recurring.  
Was a sensitivity run at all? What about bloods?
These could certainly be very informative regarding what pathogen was actually affecting the respiratory tract, the health status and immune system.  

Regards

Note: added another 2 genres of turtles.