Getting a true value quote on an older vehicle is hard to do. You have to look out in the market for your area and determine what yours is worth. There are so many varibles on it that it is a difficult job. It is very difficult to find 3 or 4 other trucks the same year in approximately the same shape as yours in an area, but that is what you need to do.
You can also find a collector and ask him or her to shoot you an offer, you can bet it will be a lowball though.
John