Do you need to have your truck on neutral to engage 4WD?

The answer is no. Whether you've got a standard or automatic might make a difference but I doubt it. Our truck however has had a lot of transmission issues among other problems and although we can put it in 4 wheel high in any gear, to put it in 4 wheel low we have to shift it to neutral and turn the truck off...it will either work for you or it won't.