Hey mate....
Currently having the same issue with my old mans 4.8 gu. We took it into Nissan and they had it for a day and said they would just put a new earth to the tank. Well that worked for a few hours and cost 180$.

They now currently have the patrol and have had since Monday and are now saying it is a power feed to the pump which is causing the problem. They said they will still need it tomorrow to fix it. They spent all of today finding the problem so hopefully they will sort it all out.

I know it may be a costly thing but you may have to take it to Nissan. If I can get them to tell me the exact problem I'll post it up.