Every so often after driving my car for a little bit i'll pull up to a stop light and i'll notice its idleing about 200rpm higher than usual. And when it does this, i'll take off and it goes to about 2500+rpm to shift unless i let off the gas then it shifts. It does this from 1-2 and 2-3. When usually it'll shift anywhere between 1500-2000 rpm. It seems to only do this when its hot outside. Any ideas?