I use the insulating sleeves/tubes that you find on late model vehicles. They use them in a lot of places, even on the A/C lines. The right ones will fit you tranny lines like a glove, are dirt cheap, and will do a super job. The self-serve or pick-a-part yards are good sources with lots and lots of choices. I keep a lot of different sizes and styles from different manufacturers and from different kinds of lines lying around. Always finding a use for them on my car or on buddy's cars on fluid lines that we want to keep as much heat away from as possible.

We have used the sleeves/tubes on fuel lines, tranny lines, p/s cooler lines, and even some wires/cables that run too close to the exhaust or headers. That helps to guarantee that over time, wires/cables that are close to the high heat sources don't eventually or accidentally touch.