Won't Rev past 1500rpm

[JoshT800]

Thanks, but the truck has only 1 speed sensor at the back, I unplugged it and the speedo stopped work. My Brother has an International with the same engine, when i Unplug the speed sensor it won't rev pass 1500 and the speedo won't work too, plug it back in and it's back to normal.

To answer Rawze: I unplugged the diesel particulate filter and it through the check engine light. The truck worked fine for weeks after that. Parked it for about a week and then this issue. Before I bought the truck, I told the company to step up the hp to 500 and make sure the DPF is deleted. I paid them $1200 to do that, but i don't think they did.

I also noticed the turbocharger speed is about 18000rpm at idle, on 1500rpm it's about 52000rpm. Is this normal?