We were kind of in the same situation, I have a 2004 quad cab Dakota with 4.7L V8, 5 speed, tow package, and rated at somewhere above 5,000 lbs towing capacity. I looked and looked finally settle on a new Coleman BH15 3,500 lbs max weight, well within the towing and weight rating for the Dakota.
The trailer tows fine up to 50-55 mph on the flats above that it struggles and any hills are 3rd gear at 40 to 45 mph. Plus gas milage dropped to 8 to 10 mpg, not much range on a 22 gallon tank.
What I realized with the trailer was it isn't so much a weight issue as a frontal area, wind resistance. Because we also have a 21 foot boat, loaded with the trailer it weights in around 4,300 lbs the pickup tows the boat great and I keep up with traffic on the freeways and the hills, I can maintain a freeway speed of 70 mph just fine.
After 3 camper trips with the Dakota went out and bought a good used 2000 Excursion V-10 with a 4.30 rear end, and 95,000 miles. Now I can go freeway speeds, up and down hills, and have plenty of room for the family. Plus gas millage is 10-12 on a 44 gallon tank.
So if I were to do it again I would go with a slightly bigger used trailer and good used tow vehicle, I would have ended up in the same price range and had a little bigger trailer.
