GPS Units = Show road steepness?

Talking about GPS units on another thread reminded me of something else I wondered if they do. Does a bicycle GPS unit show you the steepness of roads? There's an area that I frequently ride where on road has short but very steep hills, another road a mile or so east of it has much more gradual hills whilst a third road to the west of the first one is a major highway that can be ridden with a bicycle. What I'm wondering is this: if someone unfamiliar with the area got there and used a GPS unit to show those three roads, would the GPS unit show them the different gradients of the roads? Or is that another function that they'd need to download or otherwise install?

Cheers