Pre-emission ISX turbo issue

[Dakota]

I have a 2003 W900 with a 2002 ISX rated at 550hp, about 3 years ago I blew up the turbo and had Cummins put a new one on,after I got the truck back and took off down the road i got a check engine light and it derated. I took it to the next Cummins shop and they told me it was the intake pressure sensor ..that wasn't it...have replaced Barometric pressure sensor replaced vacuum line to turbo...still did the same thing... engine code says it was Turbo speed sensor...how does this happen when there is no such sensor on a waste gate turbo?... I have since backed the waste gate off by 6 turns,no check engine and no derate,but lost power and fuel mileage...