Doubt that you need a different trans cooler. If you are experiencing high trans temps you are probably experiencing an inherent '05 problem. Google "thermal feedback" or look for posts by "Killerbee". A different turbo mouthpiece and induction tubes usually fix the problem for alot cheaper than any other remedy. Try email@example.com
You can avoid reality, but you cannot avoid the consequences of avoiding reality – Ayn Rand
The Killerbee fix was not for overheating transmissions. The most common cause of an Allison overheating is overfilling the transmission. Double check your fluid level. Best to run it a little low than over full.
What were your temperatures and under what conditions?
One thing to check or just replace is the thermostat. They run on a little bit of wax, that as it melts expands, pushing against a spring, to open the water flow. If only a tiny amount of wax escapes, it will stop working right, and the engine will overheat.
Put the thermostat into boiling water, and see how far it opens. Better yet, replace it with a new one, they don't cost more than $20.
I had a friend that has a Mitsubishi, and it constantly overheated. He installed a hydraulic reservoir cooler on his engine, the thing never overheats anymore! I think the cooler has 1" lines and is only about 14" tall and 7" wide, 4" deep. The tubing makes about 6 passes, and comes out at around 120F. This cools the engine by getting rid of about 1/3 of the heat.
In the 05, the transmission temperature is dependent on cooling system effectiveness, because of the liquid/liquid heat exchange between them in the radiator. Any changes that you make to improve cooling system performance, will lower transmission temperatures.
Until we get some temperatures from the OP we do not know what is overheating. An overfilled Allison will overheat without the engine temperature beyond the limits. We need more information from the OP. From what I read I was of the impression his transmission was overheating but then what some consider too high is often well within normal operating temperatures.