From everything I've seen on thie website and others, the 97-03 cars never seem to have high trans temps compared to 04+ cars. For whatever reason 04+ cars can't cool aswell from either a lack of air flow over/under the trans, smaller cooler. GXP's transfer the engine heat into the trans aswell as having a huge oil pan, which stops alot of air flow to the trans case under the car.
Personally I would see where your trans temps are currenty at before you invested in a cooler. Also 220 is not really hot either, might be 10-15º over normal, but a trans running at 175-205ish should have a fluid life of atleast 50,000 miles.
Even after beating on my car during tuning session in the summer, the trans maybe got within 10-15º of coolant temp.
