Hi Alan,
Full PDF guide here; http://www.350z-uk.com/topic/54763-how-to-fix-the-inaccurate-fuel-gauge-pdf/
Not sure if you read that or just did it yourself. There are two senders so you have to do both but I'm assuming you did this?
Other thing it could be if you followed the guide and it's still fubar is a faulty sender. Might need a new or good second hand one to sort.
My fuel gauge isn't accurate but tbh I just rely on knowing how much fuel I have put in the car & the miles I have covered. It's a risky game though as MPG does alter depending on my driving style.