Engine losing power throwing codes 4334 and derating any ideas cummins replace the Def pump went 150 miles did it again.
Is your harness in good shape? I noticed when something goes wrong with the DEF system most of the time it is electrical, but having a repeated pump failure sounds like there could be a blockage burning up the pump. Rawze posted pictures of one truck he looked at with similar complaints (and the truck owner having spent a large amount of money with no luck) that had the DEF crystallize almost blocking the pipe where the DEF injector was.