I suppose if you have the truck disassembled it would be feasible to route steel trans cooler lines, but working underneath the tight confines of an assembled truck often make this impractical. Most trans cooler kits come with rubber line, so the manufacturers must believe it to be adequate. Plus, calculate how old you are, how long you have left to live: modern high-pressure rubber line will probably outlast you.
When building a vehicle from the ground up, I typically use hard line up to the cooler, then rubber line to connect the two. I've never had a rubber line fail.
Last edited by Jay Zed; 12/09/2016 9:07 AM.
