A little outside the OP's year range but...
I have a 2011 Ram quad-cab, 5.7L, tow package, 4x4, 3.92* rear axle. I tow a lot of stuff with it.
The following are CAT scale weights with trailers normally loaded (water, food, fuel, etc):
With my 7980lb travel trailer, I get 8-9 mpg, depending on how hilly the terrain is.
With my 6600 lb fifth wheel and 3200 lb Moomba ski boat, I got 6 mpg (I towed them both together, boat behind 5th wheel)
With my 6800lb Sea Ray 230, I got 11.0 mpg.
With my 9800lb Sea Ray 270, I got 8.0 mpg (estimate, only towed 130 miles to new slip)
Unloaded, in town, I get 16-17 mpg.
Unloaded highway I get 21 mpg (This is a frequent 350 mile trip, flat interstate the entire way).
Details:
I have self-leveling air bag suspension in the rear (aftermarket).
The large camper is towed with a Hensley hitch, sway can be a problem with 1/2 tons and 35 foot trailers.
The 23 ft boat was towed with a weight distributing (trunnion bar) hitch.
The 27 ft boat was towed with an Equalizer hitch (4-point sway control).
Truck has a 15K+ GCWR, and a 6700 GVWR.
All the rigs listed above are within GCWR. All but the short trip with SR270 are within GVWR (I exceeded it slightly but it was a flatland, smooth trip).
The GVWR will be your limiting factor, with the big camper we have to be very careful with loading, and carry almost nothing in the truck.
*going from memory, it's 3.9-something.