A lot of interesting stuff to consider. We have the Kodiak 279RBSL. Empty, it weighs 5600lbs. Tongue weight is estimated at ~700 lbs. I figure our max additional load on the trailer is 1,000 lbs. At that point our tongue weight should be 825 lbs. The tongue weight of this trailer computes to a very nice 12%.
Our TV is a 2013 Ford F150 with the Econoboost V6. The TV is rated to pull ~10,000 lbs. The combined weight is well inside the limits. In practice, we have towed 6 times so far this year, all of the trips requiring crossing at least 2 mountain passes. There have been no problems and even to me, an inexperienced tow driver, it feels effortless to tow the Kodiak. We bought the truck before we even considered owning a RV. If I knew that I would be towing, I might have gotten a HD (F250,350?) truck. But the truth is that the combination we have is fine and fun.
One other consideration (this will really upset the *power* people) is that the limits set by the TV manufacturer is not the maximum safe limit for the vehicle. It is probably 80% of that number since it is good engineering to leave a margin for safety. This is not to say that anyone should exceed the limits on your truck's sticker...just that being close to the limits does not necessarily spell doom to you and your TT.
Since we use the truck every day and we get about 18mpg without towing (9.5 mpg towing the TT), I am not sure it would make sense to get even less economy just for the sake of leaving a bigger margin.
By my calculation, we are at 70% of rated pull and about the same for weight. That feels efficient to me. And from our experience, even on 6% - 8% grades we experience no loss of power.
