need a cummin diesel expert

yes it turns out to be the trans cooler.

I got under the truck today and the tranny lines run from trans to cooler only, and the coolant lines in front out the back.

since I need to change the steel lines also and since I plan on keeping the truck for some time I will put a new one on since this one rusted out, I would hate to install a used one and have it go out in a short period of time.

Thanks for the input