If you are planning to take your car back to Fiji with you it might be a good idea to hire a relocation company, as they will be the most knowledgeable on the regulations that are relevant to your specific situation. Depending on where you are transporting the car from, it is is quite likely that you will have to pay some form of import duty or tax on the vehicle. Have a look at our Banking, Money and Taxes in Fiji page for a general overview of the tax system in the country.
Shipping your truck is likely to be quite costly and time-consuming. Road conditions in Fiji can get quite rough, which could damage your truck and make the move even more complicated.
Have you considered leaving the truck behind and making use of one of Fiji's many public transport options?