Its important to understand most techs at dealerships don't really know what the heat exchanger pump is... Chrysler calls it an auxillary water pump, and mentions nothing about the heat exchanger. The techs are trained to follow written troubleshooting steps and the intake temp sensor is one of the first things to look at. THe reason is because the computer uses that sensor and that sensor alone to determine if the air temps are too hot. Air too hot = bad air sensor according the Chrysler, they don't try to look for the root cause of the hot air.

If I were you I'd be very specific about the auxillary water pump with your dealer, and even pop the grill and show them, and explain that it needs to be running in order to cycle the heat exchanger water through. I know this sounds childish but the srt-6 is an ignored vehicle by chrysler, they have enough mass-produced vehicles for techs to learn.

Also... its my opinion that the pumps fail because the stock heat exchanger is too restrictive. The stress kills the pumps. So upgrade your heat exchanger or branch off a second exchanger in parrellel with the stock one (thanks Woody!) to relieve the work load. etc etc.