In their 2nd report of their long term test of the
5.7MDS 545RFE in a 2006 Ram TRX4
Fourwheeler magazine says mostly good things
about the Ram's reliability and road manners:

http://www.fourwheeler.com/roadtests...ram_1500_trx4/

sample quotes:

1st report
Long-Term Numbers[/align] Miles to date: 4,796
Miles since last report: First report
Average mpg (this report): 13.28
Test Best tank (mpg): 14.8
Test Worst tank (mpg): 12.13

2nd report
Long-Term Numbers[/align] Miles to date: 14,010
Miles since last report: 9,214
Average mpg (this report): 14.0
Test best tank (mpg): 16.6
Test worst tank (mpg): 9.0

In the most recent issue of the magazine
(April 2007) on the newstands
they give the 3rd report at 25,000 miles
and the fuel economy is only a few tenths better at
14.4 MPG

So the 'break-in' improvement to be expected
is about 1 MPG
over the mileage from 4,700 to 25,000 miles.

Another way of lookin at it is that the improvement is about
1 divided by 14.4
or about 7%

The 'worst tank' (9/14.4) is about 38% down (towing?)
and the best tank (16.6) is about 15% up

Another long term test of a 3rd Gen 2002 Ram
this one with a 5.9V8 engine and 46RE auto
by Car and Driver magazine over 40,000 miles

http://www.caranddriver.com/longroad...ort-page3.html

Although the C&D 2002 Ram
might have towed a bit more of its miles than the Fourwheeler Ram
this earlier model showed an overall MPG of 12
so perhaps the 5.7 with MDS is about
16% more efficient.

The Car and Driver article does not show 'break-in' for fuel economy
but it does show 'break-in' for acceleration performance
which is also in the 7-14% range.

Originally Chrysler said the 5.7 without MDS was 8-12% more fuel efficient than the older 5.9V8, and with MDS on the latest models of the 5.7 this may have gone up a bit more, but not all the credit should go to MDS. Other press releases have bragged about the 'Tailgate Thingie' improving aero slightly, and 'lower rolling resistance' tires were standard some time in early 2005. The revised headlights of the 2006 Ram may have slightly improved aero too.

For a review of a 3rd Gen Ram with 4.7V8 check this link:

http://www.usatoday.com/money/perfi/...0-ram.htm#more

where a "no break-in" model year 2002 4.7V8 Ram
in 2wd showed 13.1 MPG
and 4x4 version showed 11.8 MPG

For a heavier weight 2500 Ram check this weblink:

http://www.motortrend.com/roadtests/...fications.html

where the 2500 long term average MPG declines to 13 MPG.

to compare to other pickups:

Silverardo Hybrid (15 MPG)
http://www.motortrend.com/roadtests/...verado_hybrid/

GMC 6.0L V8 Denali 2500 4 wheel steer (11.8 MPG)
http://www.motortrend.com/roadtests/..._sierra_denali

Nissan Titan 5.6 (14 MPG)
http://www.caranddriver.com/article....;page_number=3

http://www.motortrend.com/roadtests/..._se/index.html

Multi pickup comparisons:

year 2007
http://www.edmunds.com/insideline/do...ticleId=119281

http://www.caranddriver.com/comparis...ta-tundra.html

year 2006
http://www.trucktrend.com/roadtests/...son/index.html

year 2002
http://www.caranddriver.com/comparis...ron-page5.html

 

That sounds about average for me city combigned with highway driving.