Engine surging under low boost

[720Deere]

I guess I jinxed myself 2 weeks ago by install a straight 4" MBRP exhaust. The truck has 10,460 miles and has performed flawlessly until a few days ago. It started to gently surge at highway speeds of 55 - 65 mph and boost levels of less than 10 psi. I checked the oil level and it was 1/2 quart low. I topped it off and ran it another week with the same problem. Today I did a complete service including oil, filter & fuel filters. I also figured it was time to clean the EGR valve. I have seen pictures of worse but it was crudded up pretty bad.

I have since driven about 20 miles and it feels as if the surging isn't as noticeable but it is still there. Could this be related to the lower backpressure of the open exhaust? I don't have any means to pull codes at this point, but the light hasn't come on either. Maybe I can get Autozone or some other parts store to scan it for me.

I like the sound of the exhaust minus the cat and the muffler and would hate to be forced to go back in order for the truck to run properly. I should have known better than to monkey with something that was working so good!

[tractor nut]

hate to tell you but probably needs the turbo replaced. our work truck did the same thing the dealer sais oh its an egr valve they replaced it and still did it took it to another dealer they replaced the turbo. dont know what was wrong with it but they replaced it

[npccpartsman]

It's not your exhaust. The EBP valve is in the left front of the drivers side manifold and isn't affected by exhaust size despite what many say or believe. Your surging may be from coking of the turbo if your EGR was really gunked up. Do you use Diesel Kleen or Stanadyne fuel additive? They typically help prevent this. Also, drive it like you stole it occasionally and it helps prevent turbo coking.