Read this thread, plus peruse that forum.  A wealth of information for you on the care and feeding of your truck.  This is how I educated myself about my 2004.5 since I purchased it 3 1/2 years ago:
Newbies Guide to your 3rd Gen Dodge Ram diesel truckThese are good trucks, and you can make them last a very long time, but there is a lot to learn to accomplish that goal with reliability.  As someone mentioned, add finer fuel filtration and a water separator to prolong the life of your injectors.  The finest fuel filter you can put in the OEM canister does not filter as fine as Cummins' spec -- this was a screw up on Dodge's part.  
*This*  is the filter setup I'm about to install.
Also, aftermarket oiled air filters and such are not recommended.  Use 
*this* deep filter in the stock intake housing.
If you have the auto transmission, when it needs work, find someone knowledgeable to work on it, get a shift kit and some other tweaks and improvements to the stock trans, most especially if you are towing.
Congratulations on your purchase and good luck!