Oh....the information I have.....
The QC trucks (05 and 06 only) come with the 48RE automatic transmission and are much more suitable for hauling.
BUT, I tow our 3200 lb.motorcycle trailer (6x12, single axle; 2 atvs & 2 MX bikes) using my RC without any issues. You just have to be smart about braking and shifting, etc.
The weak link with towing comes from the clutch and rear end; NOT from the engine.
If you need to tow more than 2500 lbs. regularly or daily, find something with a Cummins and have MoparBoy **** the hell out of it.
Real world MPG? I have no clue, and I don't care. I love driving the truck. $10/gal and I'd still drive it.
I put a cap on my RC (blasphemy in the SRT-10 truck world) and loaded 2000 lbs. of gear in the back. Drove to Orlando and back and got almost 20 mpg by smart driving/passing and keeping the cruise right around 72-75mph.
RedSnake is correct about the rear end gear ratios. There are a few other differences between 04 and 05, namely the front brakes.
The 04-05 interiors are my favorite; the changes in 06 just didn't thrill me. Some folks love it. That's cool, but it's not for me.
If you have more questions about the trucks, let me know.