Is it mechanical shuddering like suspension geometry or is the engine misfiring.
If misfiring and its fine when the turbo kicks in you may have a crack in the turbo hose or intercooler and be losing boost pressure.
If its mechanical shuddering when the turbo kicks in and you're generating large torque something is getting pulled into line. I had similar problems when the wishbone bushings were gone. If you jack the truck and hit the tyre with a large hammer in different directions you should be able to see if the wishbone busings, balljoints, trackrod ends, anitiroll bar bushings etc are worn.
jim
January 2010