I've heard of mechanics calling the dregs they push out of the oil gallery "turbo turds" 'cause thats what they look like !

<div class='quotetop'>QUOTE</div><div class='quotemain'>One question though. Is the turbo drive adjustable in any way? I was wondering if there can be drive slippage or whatever that could impact on performance.[/b][/quote]

the heat from expanding exhaust gasses drive the turbine which is on a common shaft with the compressor wheel.
If you are making correct boost, (IIRC, 1.1 bar/15.5 psi max) and there are no air leaks between the compressor outlet and the inlet valve, look elsewhere for your problem.
If there is insufficient boost, I suppose it could be a wastegate problem, (opening too early) or an injection problem. Remember you need fuel to burn to generate the waste heat to drive the turbo to generate boost.