First off, welcome to the forum,
This forum is full of great looking trucks, and packed with great mod ideas.
There are loads of knowledgeable and experienced people here, so expect numerous responses soon.
As for your issue, 4.7L, 4x4, 3.55 gears is not IMO, a truck for towing anything more than a small single axle trailer. With the smaller engine, and the steep gears, it will likely have enough trouble pulling itself at highway speeds, let alone a trailer.
I am NOT familiar with that combination, but do alot of trailer towing, and in my experience, the specs you gave, match the symptoms you describe.
Chances are that a full tune up, and possibly a performance tuner (AKA Chip) could render you better results, but there is no substitute for Horse power and gears!
Here's where I let those familiar with the 4.7 / 4x4 give real world advice.
Enjoy to Forum!