Ticking like a lifter? what is it?

[myredtruck]

My truck has been ticking inconsistantly but almost like a lifter in a gas motor. sometimes it runs rough coming into idle like almost a complete misfire. but it sounds like a injector misfiring to me. well i took it to bakers diesle here they scanned and came up with number 4 injector so i had them replace it and they scanned again and got number 8. well since it didnt show up on the initial scan i just took it but now the tick seems very consistant. any ideas? it also seems like it could have some more power some times. im very frustrated any help would be helpful thanks.