bulkpart.com has a HUGE tranny cooler.. something like 40,000 BTU's. A lot of guys on the 5.0 side run them. They are actually not too expensive considering how much heat they can dissapate.
Installation is pretty straight forward, no matter which way you decide to hook it up.
There's a standing argument, do you keep the radiator and it's tranny cooler in the chain, or remove it entirely. If you live in a cold climate, I suggest keeping the radiator in the chain. This will aid in bringing the fluid up to operating temperature in really cold conditions.
You can also just cut the factory lines, and run the hoses right around to the cooler. If you choose to keep the radiator in the chain, bulkpart.com also has a fitting kit you can buy so you don't have to do any cutting.
Either method is proven to extend transmission life, and will be a great start to facilitate future mods (stall converters, shift kits, etc.)