I have the 6.0 diesel. When I start from a stop, I have lots of hesitation, black smoke, all at low rpms. Once i get the rpms up its normal response and acceleration. When I unplug the VGT solenoid on the turbo, I get great response, no hesitation until I get up to 2000 rpms, but no black smoke. When I plug the VGT solenoid back in, I get bad hesitation, black smoke. It takes a few seconds but it kicks in eventually. I am not getting any check engine lights. Sometimes while the VGT solenoid is unpluged it comes alive and runs great. I am an equipment mechanic, so i just need to be pointed in the right direction. I've changed the fuel filters, and added fuel treatment.