ISX CM870 Jake Brake Repair

[same101us]

2007 Peterbilt 379 with 2 solenoid jake brake. Turbo was replaced when we did overhaul. They worked good up on till now. I noticed sometimes they just sputter before the latched the 3rd stage. I am planning on doing the first overhead adjustment after overhaul. Everything is original under valve cover. I read on here somewhere where guys are replacing the springs and the rocker shafts and i need more info how to go about it.