It's not turbo lag. The trucks have a shutter problem, it has to do with the angle of the driveline/driveshafts. There is a service bulletin for this, but I don't know how new of a truck it includes. We have an 03 here at work and the TSB specifically explained how to measure the shaft angles and shim the carrier bearing bracket accordingly. In the end, we shimmed the carrier down 10mm. The shutter got better, but now the thing eats u joints like there's no tomorrow.