IMO all 4T65es should have a cooler. ASE says ATF should be 175*F and for every 20*F you increase you cut the life of the fluid in half, and at 230*F you have the potential for valves to start sticking in the valve body. ATF should last 100,000 miles or so, but companies rate set the maintenance interval at 50,000 since they run at 195*F, right around the engine temp (no external cooler needed).