I have a 2004 ISX 500/1650. Your boost is really low. Mine will hit 35psi when climbing hills at max loads. 30psi is very common even on gradual inclines. Oil pressure sounds good, mine hovers around 40 psi. I did Rawze's EGR tuneup. Definitely worth doing, but all the sensors are close to $700 from Cummins. If you can get to the Atlanta area, take it to Haggai Automotive and truck repair. The owner is a close friend of Rawze and one of the best ISX mechanics in the United States. I just recently had my EGR cooler and oil cooler replaced there.