I don't know anything about caprices. That could be possible because it's not a performance car and the stock ECM tune is probably not very efficient at all. I would still be dubious. But the Z is a pure sport car, it comes very well setup from the factory, which is why it's more difficult to squeeze NA hp out of it.
Go to the uprev website and find the nearest licensed tuner, give them a call and see what they say.
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I am here:
http://maps.google.com/maps?ll=28.354338,-80.686554
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