To me gas mileage for a utility vehicle is last on the list of
priorities.  Its a minor expense in the overall cost of ownership.

The 5.7L Hemi is not strong enough for your 8500lb trailer.  Tow
capacity is about 9150lbs.  You'll quickly be over the trucks GVWR and
be under powered.  I have a Hemi Durango and pull about 5,000lbs.  It
does very well but I wouldn't want to go much heavier up steep grades.
For a 8500lb trailer get the diesel.

For reference my Hemi Durango gets about 15mpg city, 18mpg highway,
10mph towing.

  Hemi economy, that's funny.  Kind of like jumbo
shrimp, military intelligence, and accordion music.
The two words just really shouldn't be used in the same
sentence.  ;)

  If you're going to pull a lot, get the diesel.  In
general use, the diesel and the hemi will cost about
the same to run.  But when you start towing, the gas
engine will suck fuel like there's a hole in the tank.
   The diesel also has a lot more torque.  You'll
really appreciate that  when you're pulling a long slow
hill.
   One last thing, the diesel is turbocharged.  It
makes about the same power at 12,000 feet as it does at
sea level.  Can't say the same for the gas engine.

I just traded my 2003 2500 Hemi for a 2005 Turbo D. for this reason. There's
no comparison. The hemi is fun as hell to drive around(12-14MPG) Towing
(6-8) I would never have taken it to the mountains or even rolling hills
though. My deisel yanks my 12600 pound 5th wheeler around like a step child.

Diesel Diesel Diesel.

Now, with that out of my system, talk to a dealership and find one that
will let you test drive one over the weekend to see what kind of
mileage you get.  Sure, you can't try it with your 5th wheel on it, but
it'll give you some kind of idea.  Also try one, in similar
circumstances, with the Diesel.

After going from a 98 1500 360 extended, short box, 4x2 to a '02 2500
Cummins regular output (not the HO) 4x4 extended, long box and getting
better mileage than the 98 I'm sold on Diesel.  I don't pull much or
often but when I do it's infinitely better than the old gas one.

If you get the Diesel I'd recommend gauging it out (meaning installing
a fuel pressure gauge (to see what pressure your injector pump is being
fed; if the lift pump goes bad it can eat your injector pump (based on
my experience with my '02)), boost gauge, exhast gas temp (pyrometer)
gauge, transmission temp, oil temp, and differential temp gauge) so you
know what it's doing.

I hear a lot of suggestions of running anything to help lubricate our
"Americanized" "dry" fuel (low sulfur fuel; i.e. low lubricity); so use
some Marvel Mystery Oil or some of the (I'll get this wrong) Power
Service or whatever Diesel Kleen/anti-gel, whatever additive, to keep
the fuel system in top shape.  The stuff is dirt cheap, and the extra
power and mileage you'll get out of that Diesel engine should more than
make up for the little extra effort you'll put into it.

That's what I think.

HTH

--HC

As has been noted the subject of this thread is an oxymoron.

Anyway, I have a 2004 2500 4x4 reg cab hemi with 5sp standard. In 15K
miles the best ever tank was 14.5 mpg highway with no trailer or load.

Overall average is about 13.5. Towing a 6000 lb trailer I get about 10
mpg and our friends with a Cummins diesel and a heavier trailer leave
us in the dust going up hill while using less fuel.

Woody; 95FXDS

We tow a 7600lb trialer (loaded) with a Hemi in a 1500 with a 3.92 rear end
and auto.  Average mpg is 10 while towing.  worst case has been 7.25, best
was 11.5.  Average when not towing?  15.  Mountians?  No problem.  Do I try
to play crotch-rocket with it?  No.  When gas prices were about $1.50 I was
told to figure about 81,000 miles as pay back time for the extra cost of a
diesel.  I don't know what it would be now.  Just an intersting note.  I can
leave a diesel in the dust while towing and he is empty.  FWIW  And I don't
have to put up with the God awful smell.