DMorrill. .
As Kenny has already said its well known that timing could be one of your issues to reduce fuel milage and cause a lack of power. Other things to check off the top of my head are as follows...
-Make sure the truck is freshly serviced(new air filter,fuel filter) so you have a good basline to begin with.
-Make sure you do not have a bad fuel problem. Fill the tank and add a quart of your favorite additive and a anti-algae additive(such as Bio-Con) which will add to your good baseline to begin working with.
-The fuel return line-Follow back from the P7100 and you find a section of rubber hose that is well known for cracking and allowing air to seep into the system and kill milage and power. It will also cause a white haze of smoke uopn starting and make the truck harder to start initally.
-When were the valves adjusted last?. They are supposed to be adjusted every 24,000 miles on a 12 valver. This has also been known to kill milage and power.
-Have the fuel pressure checked and see if its possible that the lift pump has getten weak. Although its not a common problem among the properly valved trucks if you can visibly see wet or leaking fuel around the boot on the primer pump on the lift pump then possibilities are it may be weak. Most owners never have a problem with them,but,I have seen some fail even before 100,000 miles.
-Check the pre-filter bowl screen(located down near the lift pump) as they have been known to get dirty and also kill fuel milage.
-Have you checked all the turbo boots and clamps for tightness and made sure none were allowing boost pressure to seep out. They should be checked at each service for tightness.
-Look around the bottom of the air horn as I have seen some which while being boosted hard push the intake gasket below it out and leak pressure. Its a relatively easy and cheap fix if it needs done.
-Another area to look is the exhaust manifold and the gaskets where it attaches to the block. The 12valves have long been known for the manifolds expanding and contracting bad and at one time were being replaced by Ma Mopar due to this. When they do this they will push the gasket out of the sides of the manifold(usually facing the front of the motor)and it will allow the motor to not build as much boost and add to your fuel mlage and power woes. The fix for that is either pull the manifold,replace the gaskets and add Mopars poorly designed fix or buy a ATS 3 piece exhaust manifold which is the best answer.
Hope those give you some points to begin with and let us know what you find wrong. It is not "normal" by any stretch of the imagination for a 12v to get the milage your quoting unless its a 4. 10 rear equipped truck. Even with the shorter gears it still should average around 17 empty. A good place for you to look is Dave Fritz's website which I'll add below for you as he has alot of good info for you as a newbie. Hope I wasn't too windy and gave you some ideas which will help... ... ... Andy
www.dodgeram.org
On edit...
BTW,I see your in the Northwest and in the Northwest Bombers area. I'll add a link for you to their website as many of them can help you get it straightened out and purring like a kitten. They are a bunch of top notch owners and area always willing to help new owners. One last Thing,Welcome to the TDR!.
http://www.nwbombers.com/
Attention: TDR Forum Junkies 
to agree with Hammer. . . in most of what he wrote. 
