Well it looks like everyone covered most of the bases. What does a secondary gauge say when the temp gauge goes up while towing? Forgive me if you already mentioned it but does the scanner data match the temp gauge on the car? Depending on how much you are towing it may just need a cooling system upgrade. Would a different tune help it run cooler? If the condenser isn't restricting air the only other things I can think to check are any factory shrouds the help air go through the radiator and not elsewhere.