Can I add the Tow Package

Hello everyone. I just found this forum and man is it filled with great information. I have an 07 4x4 Nitro SXT with the 3.7 but it did not come with the factory tow package. I have had a class III hitch installed along with a trailer brake control. I am planning to pull an ultralite camper that weighs around 3,600 pounds. I was wondering if I should have the heavy duty engine cooler and power steering coolers added. I stopped by my dealership and the parts manager said he did not show these items in the book to order. I don't know if I need them, and if so, how to even get them. I have a weight distribution hitch, which should put me at the 3,500 pound towing max, but I would like to know what I need to do to get to the 5,000 pound max for peace of mind. Any help is really appreciated.

thanks,
spook1