Would anyone hazard a guess on what sort of fuel mileage a 2wd 3.0 diesel would average-would 5mpg better than a 4x4 3.0 be reasonable?

I would say no- these engines become pretty consistent MPG wise loaded with vehicle weight or not- diesels love to lug and 300 to 400 lbs of extra 4WD weight is not going to make a difference--
If some one does not come out with a F/S SUV soon the CRD GC is going to be my choice for the next SUV next to my Liberty and while MPG's are important- I feel going to the 4WD version is not going to make any significant difference.

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2006 CRD LTD 2.8L VM Motori turbo,CAC, 100K-new timing belt
ORM-SEGR, Trans cooler, CLIII hitch front/rear, Journey HD controller
Mopar skids,"Stone Soup" rails, KK clevis fork 1" mild lift w/Daystar stops
215x85 LRD BFG Commercial A/T's, Rola Rack, V6 airbox, Fumoto valve
10K winch, B5 Biodiesel (ULSD CP3 lube)
Its a Diesel baby!

Tnks, I would agree that the weight would not make a difference but as I understand it the GC is awd with a selectable low range, so it would seem that not driving the front would have to make a difference, ?

The 2wd would blow big time in the winter but if the extra mpg are there it might be worth the aggrevation.

I did a little non-scientific test in November after the winter blend was out, alternated weeks driving in fulltime and in 2wd and found It took about 1/2 gal more per tank. Conservatively, thats 10mi in 350mi (my weekly mileage) is less 3% difference. which is in the noise (less than the margin of error of this unscientific test.) The combination of driving in FT and the weight difference may be around 5% lower mpg, worse case.

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2005 CRD "Ol' Blue"
Red Ryder carbine-action, two hundred shot range model air rifle with a compass in the stock and this thing which tells time.
My build page- RL Komodo Rear and TJM Front Bumper, armored, lifted, JBA Steel D30, 4.10s and ARB air lockers.