Ok first you'll need this, think of it as your online bible.
www.dodgeram.org
next,
ETC= non-HO motor, they can be a 5spd which is reffered to as the DDX or can be an automatic truck which is a 47RE.
ETH= HO motor, they come only with the 6spd which is reffered to as the DEE
PE= power edge products they are an aftermarket vendor.
PE EZ= EZ is a boost module "box" that is made by PE
PE comp= agian this is a fueling box made by PE
DD I's II's III's. . etc. these are extrude honed injectors produced and sold by Diesel Dynamics
275's another Bosch injector originally used in other applications, that is swapped out for performance reasons.
DTT= Diesel Transmission Technology, a top notch transmission performance shop ran by Bill Kondolay.
hope these help you get started...