Cummins ISX 500 issues

How's it going guys, I'm having some issues with a truck I run for work. The truck itself is an 05 378 heavy spec triaxle tractor, 18 speed, with a 500 ISX. The truck spent most of its life pulling superloads (bridge beams), and from what I told has a cummins "X" program in the computer, which was supposed to have turned up the torque and made it about a 525. I started running this truck around June when it was repurposed as a lowboy truck, so while it's not pulling superloads anymore, it's still not uncommon for me to be grossing 130-140k lbs. just recently, the truck started having issues, it seems to be down on power a bit, and when I'm loaded and I to a pull, it will spew excessive black smoke between 13-1600 rpms, then the engine light will come on, smoke will clear, turbo seems to spool up more, but te light will only stay on for a few seconds, then when it goes off its back to smoking and being down on power. We took it to the shop and they replaced the egr valve and egr pressure sensor, but it still does it. Truck is not running excessively hot, in a hard pull with the fan on the water temp will creep up to around 205-210 but that's it. I was pulling a mountain this morning at arouy135k, and it was constant smoke and engine light on off on off, and did the same rolling down the interstate with my foot stuck in it, I I also noticed the fan seemed to be kicking in and off eradically on the interstate. The shop is befuddled because the light doesn't stay on, and the couldn't make it act up with an empty trailer (46k gross), even running it hard, lugging it, and everything. I'm at my wits end and was hoping maybe someone on here could give me some insight, thanks in advance for any help!

 

I'll see if they can order me one, I wondered if that could be causing the issue. It just seems weird to me that the turbo actually spools and smoke clears up when the engine light comes on, it seems to me it should run worse when the light is on, not better, but I really don't understand all the electronic workings of these motors yet

 

I'll check the sensor, I don't know if it can be cleaned or not to see if it acts a little better before buying a new one. The shop had the computer hooked up and drove it with an empty trailer (46k gross) and said they read 25lbs of boost, which seems low to me, but I'm not sure if their computer would be reading off that sensor or not

 

I'm not sure, they didn't say about that, I know before everything was done it'd throw a 2272 code once in a while, but that hasn't happened since the valve was replaced, and they said they can't even pull stored codes, even though it is blinking the engine light in a hard pull, it never stays on more than 3 seconds though. It's not too bad empty, although I can make it act up, loaded in a good pull though it will really act up. I paid attention this morning and it seemed like top end was nonexistent, I was pulling a mountain at around 90k and would downshift at 1400, so then I'd be higher in the rpms, and it just seemed like it fell way too fast, like there was nothing there, but when it got down to 14-1500, it would smoke, but hold steady at that rpm

 

They pulled the stores code again today, checked a couple egr tubes to make sure they weren't plugged, and now they're thinking either actuator or turbo itself, but they're gonna have a cummins tech come in and hook it to insight and run a couple test to make 100% certain before they start throwing parts at it