Orange orchard transport railcar - GIF

[BuffaloJohn]

From that I can see there’s a chain between the rails…so a little carrier connects with something under the truck and drags it up?

I don't think it is dragged up, there isn't a pulley or even enough material to hide a pulley at the top. I looked and the space between the rails is often open, even at the top, so there would need to be something in the center to balance the pulling force.

I think the cart's motion is powered by the cart with a simple friction drive and the cart rides on the rails. Possibly, the friction drive is along the horizontal axis, a wheel on each side of the rail pushing toward the middle. It could even be a friction wheel on the underside of the cart rather than horizontal - that would grip even better and would also match some of the features of the rails... The cart's wheels spin in the dirt when it gets to the top and the velocity doesn't appear to change (all guessing from a really short video).