ISX Turbo issues

I have a 2003 W-900 with a pre-emission 550 ISX, it has a waste gate turbo, I keep getting a check engine light for turbo speed(there is no turbo speed sensor never was). The turbo was new in September installed be Cummins and been having issue ever since. I didn't have any problems before new turbo was installed.
When check engine light come on it derates the engine,always happens in a hard pull going up hill,coming down hill light goes out and were back in business. Have replaced engine pressure sensor on the intake and installed new ambient pressure sensor.Have had it back to Cummins and Kenworth ,they scratch there heads say i don't know and hand me a bill for there time,anyone have any clue as to what is going on,or how to fix the problem?

 

That's all been checked, blew air through line and watched waste gate open ...

 

Files were updated,have had KW dealer b check perameters,they could find a reason for it to act up,this is a permission engine.....built before egr was instaled in the newer ones