@Margaret, it is torque that drags your load down the road. So, yes, it is important. Equally so is the weight capacity of the TV. And frankly, for both, more is better in all cases, not just because it means you could drag a bigger/heavier trailer, but also because it will mean being able to keep up with traffic going over mountains.
In the final analysis, you have to have both towing capacity/payload capacity, and the torque to move those loads. Don't discount any of them.
Diesels have inherent advantages, most notably in delivering more torque, and that at lower rpm, which is a big advantage when dragging around heavy stuff. But sometimes the manufacturer offers a bigger gas engine with more torque.
Some people tow with Expeditions or Suburbans. Jeep Grand Cherokees, Mercedes, BMW, VW, and Lexus SUVs also work. Some of those are more capable than others.
I've been using a Jeep Liberty (model now discontinued) and just switched to a BMW X5 diesel. It does a splendid job with our 5,000 lb gross weight 21 foot TT, a trailer well within the X5's payload and towing limitations. And yes, BMW says no weight distributing hitches. But my X5 came with self-leveling air bags in the rear and doesn't need WD.