what does it mean when your truck starts to lock up when you're turnin with an 2000 lincoln navigator

Is that all-wheel-drive? You might have some binding going on. There is should always be some friction in a turn from the viscous transfer case but if it is really binding up, it might be worth checking out out that transfer case. Friction-type cases are sensitive to the fluid that is in them.it might be worth changing the fluid inside.

It will do this on dry pavement if in 4hi or 4lo. If you switch to 2wd or Auto it should work better.