I've been there, attempted to tow a 21' hybrid that typically averaged ~ 4000 lbs loaded and ready to camp with our 4.0L V6 Explorer ... sure it towed it but so too could a lawn tractor. In reality, out on the highway that V6 could barely get out of it's own way ..
Our experience wasn't quite that bad, but somewhat similar; we had a V6 Explorer of 2002 vintage, pulled a popup very happily with it but then upgraded to a hybrid (HTT) trailer. What a difference! Living in the flatlands then, we took it out to the Badlands once, and driving into a fairly stiff (25-30 mph) headwind, we had difficulty maintaining 55 mph (in a 70 mph zone), and our gas mileage plummeted to something on the order of 6. We knew we'd never get this combo into the mountains, so we upgraded the next year to a big V8 1/2 ton pickup. MUCH better.
