Slopes and Movement

[triangular_cube]

If the vehicle is only going to traverse 20 or 40 meters of hill at 10% grade, the time it takes to do so within the framework of a 15-20 minute turn wouldn't matter to add extra movement costs.

That makes no sense. Movement points are variable division of of time relative to a given unit. Thus if a units slowed, whether voluntarily or by circumstance, it expends movement point commensurate with the time required for that particular event.
 

And as triangular_cube points out, PG hills do not represent "sharp changes" in elevation.  

The hexes are 200 meters across, the elevation change is 20 meters. With the change concentrated in one hex, thus any effects are concentrated in that hex. Otherwise you end up stupid stupid stuff like the "or will move" clause in the efficient split move and fire rules.

Nevertheless, reality arguments aside, we now know, from AP, how the rules on this matter are to be played.

Not exactly. It looks like cop-out by Dr. B to me. While I do respect Daniel and his opinions, he didn't design the game or its current revision. I would point out that the rules also make assaulting troops wait in their transports, and when they unload it still takes another 15 minutes to get into the fight. (Remember unloading is a movement action.)

A reality question is, relative to the 1½ mph trot by infantry, would it take a truck about 5 minutes to go up a 10% grade over 200 meters? Would it be more reasonable to consider 5% over 400 meters? That is also about 5 minutes.

P.S. I noticed you did not explain your previous reasoning.

I can't speak for all the other things you two are discussing, but the assumption that the elevation line represents a sudden increase in 20m within the hex is kind of what I mentioned by the series artwork waffling over the years. Early modules using these lines tended to have large splotches of area encompassed by a line, rather than small, discrete, and increasing areas with more than one elevation line which we see today. The newer stuff embodies more of a hill, whereas the older stuff (Battle of the Bulge, Beyond Normandy) seem to really just be a very abstract "this area is 20m higher than that area and we had to draw the line somewhere for LOS" type thing. In the latter case, that 20m rise may be over the course of 10 hexes for all we know, they just had to draw a single line somewhere for game purposes. 

Thats certainly reading a lot into the map artwork that may not be there, and the rules comment that they are gradual, not sharp rises. Feel free to disagree on that. Its just an opinion. The current map designs as said, don't really share that interpretation and usage. 

The rule itself of the road moving units not adding the extra hill cost may be an artifact from that time, and notably the text, as mentioned comes from the module rules, but it was the module that introduced this terrain type. It seems we have the core rules saying to use the road rate, and the original elevation lines rules saying specifically to use the road rate when confronted with elevation lines. To play RAW it seems to be the case to do so barring someone bringing forth an actual new rule that says otherwise. 

Realism aside, we all know the movement rates in PzG are a bit wonky for gameplay purposes, with vehicles moving much slower than they are capable of. I don't see how a truck exerting more effort to go over a grade on the road really makes that much of a difference when it comes to being able to drive the speeds we are talking about in PzG, but that is its own can of worms