Trailer Life posts the tow ratings for various vehicles by year:
Trailer Towing Guides | Trailer Life Magazine
The dealer said he would add a transmission cooler and upgrade the wiring for us at no additional cost...
IMO this typically means that particular year did not come with the "Tow Package" and therefore it would have the lowest tow rating listed in the Towing Guide. IMO dealers are no use giving you the correct tow rating info so you will have check each VIN with the manufacturer. (Don't make assumptions using the Towing Guide either - check your VIN before buying...)
Before we got our Ram 2500, we looked at Full Size SUVs including the Navigator/ Expedition. After much research, IMO the Nissan Armada was the best choice for a variety of reasons. It had the best tow rating of the 1/2 ton SUVs & fit in both bays of our garage vs. the larger 3/4 ton Suburban or Yukon XL. A co-worker has an Armada & my wife could see herself driving around in one vs. the larger 3/4 tons. Some folks on this forum tow a 7,500 TT with an Armada, and seem very pleased with the experience - although I am sure they are maxing-out their payload & GCVW.