It fits but the plastic neck on the truck has a crown where it steps down. So while the cap fits snuggly in place, the seal around the neck of the filler port is not sealed as well as it was on the 4th gen.
This is the one I have from Mopar. The black one that used to fit the previous YM's won't fit. If you want one google it you can find it cheaper than $25 it does have a tether strap. I think they make better ones...I was only looking for a dust cap.