It could be the actuator is not setup correctly, or the turbo, these arn't a DIY job really, thats why a rebuild is costly, as said the balancing is the hard part and is really a specialist job, I guess with the 'Ebay kit' you are merely replacing seals etc?

You can get someone to rebuild your turbo for you, remember if you do decide to uprate it's not just a simple case of 'bolting the new one on', you will need a new chip etc, and unless you have more power in mind, there really is no point!

Martin