If your tires are an inch taller than stock, you are travelling farther than
what the odometer says (and faster than what the speedometer says). Your
mileage probably isn't quite as bad as you think.

On my Ram 5.2 Magnum 4X4 it has the first two that you did and then added
the Mopar performance computer (you may already have this on the Hemi??),
spacer on the intake and an MSD ignition system. Milage went from 12 to 17.5
if you are easy on the accelerator. I also have slightly larger tires as you
do and my speeds are raised by about 5mph at 70. At 70mph I am actually
doing 75mph so actual milage might be slightly higher. I doubt you will see
as large an increase with the Hemi as I did with the 318, but it may help
some. I did add a shift kit to the OD tranny at about 170,000 miles when it
needed a rebuild (damn those Dodge trannies just don't last....:-) and it
now has close to 175,000 miles on it and it still runs like new with oil
pressure at 40-50lbs and no oil usage between changes every 3,000mi or so.
The modifications were done at around 50,000mi or thereabout.

Ed

You put on a wider, taller, heavier, tire with a more aggressive tread,
that would cost a couple of mpg with the added rolling resistance and
rotational weight. You also raised the truck higher, that put more air
passing under it. The K&N was waste unless you did a bunch of engine mod's.
Your probably jumping on the gas to hear the exhaust and the woosh from the
K&N.

You have a couple of options imo. Realize it is a 4x4 truck with a hemi in
it that sounds nice but gets shitty mileage and enjoy it. Or dump it and by
econo car. It is what it is.

K7N is a waste of money

This is hurting not helping MPG, especailly in town but many never
figure this out. It has to do with letting exhaust blow off too
quickly from cylinders because the engine sets its power for expanding
gases, not explosions. Dual exhaust hurt more than help MPG in urban
driving and it is a toss up if they help at all on highway because
modern engine are well tuned from intake to exhaust and when you start
hacking, MPG can take a dump.

This did not hurt

This hurt because the tires have a bit more rolling resistance and
drag

Hemis can be real gas hogs. Engine with torque peaks above 4000 RPM
are seldom their most efficent at lower RPM's and this engine is one
of them.  You have a few more things hurting you. First and foremost,
your truck is ALWAYS dragging the front differentail and drive shaft.
Even when not in 4x4 it is locked to wheels and consuming power.
Figure on at least 1 MPG or more lost because of this drag. (even more
in cold weather) Dodge is the only Detoit truck maker that does not
have a front axle disconnect ( the left it out to save them a few
bucks while potentailly costing you over 1000 bucks or more in extra
fuel over life of truck) so they will always do worse than competion
on MPG in 4x4 models. One thing you can do is use better fuel as 87
octane is a joke in that engine and it compromising power and MPG.
Also run tires at near max pressure and change lubes in Tcase and
axles if you have not already done so but do not expect miracles.  
-----------------
TheSnoMan.com

Howard,
Your truck should be getting between 15 and 17.5 MPG depending on your
driving habits. What was your mileage before the mods? That would be a good
indicator. Secondly, the K & N will flow more air initially, but the
filtration ability is no way as good as the OEM arrangement. Furthermore,
over time, as dirt is gathered, the K & N will flow LESS air than a
partially clogged factory filter. It would be wise to hook up a manometer
between the air filter and throttle body and watch for vacuum during use,
then you will know for sure. Additionally, if the exhaust has much less
backpressure much of the ingested fuel could be exiting the engine because
of reflected vacuum. This you would see as unburned hydrocarbons in the
exhaust. Using a 4 gas analyser will show that as well.
Steve