My 27' 261T (rear bunkhouse, front hybrid-queen tipout) is under 4000 lbs dry. Under 4500 lbs for a non-hybrid 28' doesn't sound odd to me.
600-1000 lbs over dry weight is a good estimate of loaded weight, depending on how you pack and length of trip. Using 800, that's about 5300 lbs. That leaves about 900 lbs for passengers and cargo in the truck.
I would only do this if you you are sure you will remain on only generally flat areas, and camp a low percentage of the year. Otherwise, should have got the Hemi.
For reference, my Mountaineer V8 has just a tad under 7,000 lbs max tow rating. It has (probably) a shorter wheelbase than the Durango, but it's a smooth tow with the Equil-i-zer and Prodigy.
thebrakeman ('70), DW ('71), DD ('99), DD ('01), DD ('05)
2004 Surveyor SV261T (UltraLite Bunkhouse Hybrid)
2006 Mercury Mountaineer V8 AWD Premier
Equal-i-zer WDH (10k), Prodigy Brake Controller