Truck in warm weather

[CanadianZ71]

For the most part my truck runs great, with the exeption of a little rough idle that I can't seem to get rid of. I do, however, find that when the temp rises the truck runs worse. Yesterday it was a warmer day (25C) and I was driving around the city, typical stop and go traffic and the truck started idleing even worse and when I stepped on it the engine seemed louder and there was not as much power as usual. I experienced this last year as well when on holidays and drinving in 30C+ weather. It never seems to do this in cooler temps and I have not gotten a SES light. I am stumped...any ideas? Oh yeah, engine temp never gets into the red or out of normal operating temp.

[bigtruck21]

the colder the air, the more dense. More dense oxygen=more power out of the engine. But too cold means sludgy gear oil and more drivetrain loses.