I've been doing some research on the "Hot Oil" message on my dash. It always comes on when I'm in 4hi or 4lo for more than 30 minutes. After reading multiple threads from here and different forums, I learned that I will need a transmission cooler so I don't tear up the transmission. My question is do you know of any good coolers? How much do they run? Easy I install or should I have a mechanic do it? I have a 2007 automatic by the way.