I don't mean to be harsh, but it's important to look at financial issues with a pretty cynical perspective.
You have 5 years to go to pay off a vehicle you've already had for 3 years? Am I reading that right?
It is very difficult to change vehicles without taking a financial hit, so you have to look at the numbers very carefully before taking that route, but it sounds like you have an unfavorable loan on the X5. In a perfect financial world, one would rarely finance a depreciating asset, but few of us live in that kind of world. I've never bought a newish vehicle with cash. That said, it's usually best to get the shortest loan that has good terms.
Just guessing from the age of the X5 and the length of time that remains to pay, you may not have any appreciable equity in the vehicle. Is the balance on the loan near or above the private-party resale value of the vehicle? If that's the case, all you'd be giving up is your emotional attachment to it. If you have some real equity, it may be a different decision for you.
If you do go for the Nissan, the best bet would be to put a fair chunk of that $200 into paying the Nissan off early, then keep it until it starts to cost you as much as a new truck payment. If you keep the X5, try to pay it off early. 8 years is way too long to finance a truck, and pretty much any consumer-focused financial expert will agree. (Vendor-focused financial experts will of course tell you to go for it and keep trading up, it maximizes their income.)
Il Carriaggio ó 1975 Argosy 24 | Il Progetto ó 1976 Argosy 28 Center Bath | WBCCI# 15566
He has all of the virtues I dislike and none of the vices I admire. ó Sir Winston Churchill