Are you viewing that temperature via the gauge on the dash or another way by chance? You can go to a 60/40 water to coolant mix to bring the temps down some. A larger trans cooler may help a little, it will help the trans more than the motor temps. Does your truck have an engine oil cooler too? If not sure, are there 1/2 inch lines running into the radiator tank on the driver's side?
@Doubeleive Wes, did your Denali come with the little 500 watt fans or was it just the fewer blades? Thinking of ways Kirk can cool his truck down while towing. Show him your Tru-Cool if you don't mind.