06 24v cummins injector pump
 

any ideas to why a 3 year old injection pump may go bad?

CP3 would go if bad fuel was run through it. Otherwise if it had to pull fuel for a long time because of a bad lift pump but they are in general very good pumps!

Water, solids, crap fuel. ULSD is terrible for water and the stock filtration is inadequate. Your fuel source is the major suspect if indedd it has gone bad.