I have the ram w/ the 5.2/3.55/auto combination, AND the factory tow package, and I've been under-whelmed by its performance, even though its "rated" for 7200lbs. My trailer is only 3500lbs empty, and I don't know exactly what it is loaded, but I doubt its much more than 4500. Anyway, its pokey in the hills. For some reason, I had it in my head that I had a 3.73 rear end, and was kind of surprised at its "pokey-ness"...when I double checked, I found that it has the 3.55, and "that explains it!".
My last truck was a dakota w/ the 3.9 engine, BUT it had a big rear end. I never towed anything of any significance w/ it, but I did have it overloaded on more than one occasion, and I couldn't detect ANY difference in its handling or acceleration. it was like the load wasn't even there. Mileage was crappy, full or empty. That's what a beefy rear-end will do. and even though the engine was relatively small, I had a snow plow on it, and that little truck would push snow like nobody's business! And I've plowed w/ much bigger trucks for other people. The Dakota was more capable than some of those.