As others have asked, you don't say what temps you are seeing. They may be normal. If I read your statement correctly, you said you pull over and try to cool it off. That may be detrimental. When you pull over, you lose air flow and will often cook the transmission, doing more damage than just continuing to drive.
You may need the radiator cleaned as stated by another and you could have a transmission that is not locking/unlocking the torque converter and causing issues. First though.....let us know what temps you're seeing and hopefully they are numbers, not a line on a cold/hot gauge.