I'm not sure of the gears? But im thinking around 3.90. I have the sport model if that matters? Im not comparing it to anything unparticular, just seemed and I would have thought it would have more umph t it for having the hemi and the power its suppose to. I was told it has the most power in its class for that year? I have 76xxx miles on it,so I don't know if it needs tuned up? It runs great and has tons low end torque. It didn't do to bad on flat ground. But the hills/mountains here in Washington gave it a challenge.
I don't buy the 3.92 gears unless it was either special ordered with them or it has 20" wheels.
Either way, unless you expected it to perform like it was unloaded it couldn't have been as bad as you think. You were likely between 6500 and 7k which is only about 1k-1500ish shy of your max towing capacity.
Can't expect it to run 0-60 in 6-7 seconds pulling that much weight. And hills/mountains? Forget it, you would be very hard pressed with a brand new truck to maintain 65 in the mountains.
When I pulled my current boat in the mountains with my '04 2500 5.7 with 3.73 years it never got above 60mph running it to the floor. You have to be realistic of what a half ton with probable 3.55 gearing can do.