I see that you are located in Colorado; I am thinking that you are going to work your truck pretty hard around your parts pulling this trailer. You do have more power with your 5.4L 3v versus my 5.4L 2v, you also have a 6-speed transmission which is a BIG improvement over the 4-speed on our van. It sure would be nice to be able to take the rig for a test spin before you purchase it. You could always find a #7000 trailer locally to tow around to see how it pulls. Just be aware that there will be a night and day difference pulling with a Hensley Arrow versus a standard equalizer type hitch especially with your ½ ton vehicle. With this test you will be most interested in how well the engine and transmission works pulling the rig over the mountains not how well it handles the road and wind. With all this said I would not pull this trailer with your rig without a Hensley Arrow, Pullrite or Propride style hitch.
I did find a 2003 Jayco 324G trailer for sale, it is in Canada but it might be worth your drive. http://ottawa.kijiji.ca/c-cars-vehicles-RVs-campers-trailers-travel-trailers-campers-2003-Jayco-Quest-M-324-G-Travel-Trailer-or-Park-Model-w-Bunks-W0QQAdIdZ476270594
You can see that they list the trailer weight at #5380. I can tell you that our trailer tipped the scales at ~#7200 with the tanks pretty much dry. We were on a one month vacation going out west and we were very loaded down with provisions. I ended up weighing the rig at a truck scale and found that we were #200 over our rear axle weight rating. I ended up moving everything I could out of the van back to the trailer. You need to pay attention to the tongue weight of the trailer because this weight goes right onto the real axle. This is the “Achilles” heel of your truck. The Hensley Arrow adds to this weight but is well worth it. I ended up exchanging the #1000 load leveling bars that the previous owner had with #1400 bars. This moved more weight to the front axle and back to the trailer. I believe that you have an air bag rear suspension that will help you out with keeping your rig level but it does nothing for your rear axle weight. Keep this in mind with whatever trailer you purchase.