Climbing + Difficult Terrain stack.. but everything you want to climb is also DT.

Climbing says that climbing costs an extra foot of movement (2 extra in difficult terrain)

Difficult Terrain gives some examples of difficult terrain, including a slope of 20 degrees or more. 

So basically, anywhere that you would be considered to be "climbing" would also be difficult terrain, and therefore always costs 3 feet of movement per foot moved.
Unless you have a climb speed -- in which case it's still difficult terrain -- you just don't pay the extra 1 foot for climbing. 
You'd need a way to also ignore difficult terrain to move at full speed while climbing

What do people think? Is that the intended way to read these rules?

The "slope of 20 degrees or more" means that you are moving horizontally on an inclined surface. When the surface is mostly vertical, you are climbing and it is no longer difficult terrain.

That sounds like a reasonable resolution, albeit without specific guidance from the rules.  "When you're climbing" is somewhat vague.  At what point do I go from clambering up some difficult terrain to "climbing"? Is it 75 degrees? 80 degrees? Is it "whenever you need to use your hands to aid your traversal along an incline"?  

Following on from that:  I'm curious what you think would count as difficult terrain while climbing? I mean -- I guess there might be a situation where you want to climb over an enemy.  The "heavy snow, rubble or undergrowth" doesn't really make sense, since that's impeding your horizontal movement. I might consider something like a crumbling cliff-face where you have to be careful in case you put your weight on something that gives way as "difficult terrain while climbing".  

Quote from eRaz0rHead >>

That sounds like a reasonable resolution, albeit without specific guidance from the rules.  "When you're climbing" is somewhat vague.  At what point do I go from clambering up some difficult terrain to "climbing"? Is it 75 degrees? 80 degrees? Is it "whenever you need to use your hands to aid your traversal along an incline"?  

I would say any time you are moving more vertically than horizontally. 

Quote from eRaz0rHead >>

Following on from that:  I'm curious what you think would count as difficult terrain while climbing? I mean -- I guess there might be a situation where you want to climb over an enemy.  The "heavy snow, rubble or undergrowth" doesn't really make sense, since that's impeding your horizontal movement. I might consider something like a crumbling cliff-face where you have to be careful in case you put your weight on something that gives way as "difficult terrain while climbing". 

I don't know that I've ever used difficult terrain while climbing. Climbing through a small opening would be fair, I suppose. I do feel the difficult terrain rules are written with the assumption that you are moving horizontally. 

I think the example mentioned for Difficult Terrain would be an incline where you can't climb given that climbing and walking are two different movement speeds. Thus I wouldn't say all climbing is difficult terrain and in fact you could probably have a climb that is also difficult terrain.

Quote from eRaz0rHead >>

Climbing says that climbing costs an extra foot of movement (2 extra in difficult terrain)

Difficult Terrain gives some examples of difficult terrain, including a slope of 20 degrees or more. [...]

 I don't consider a wall or a cliff to be a slope.

Personally i don't find Climbing to always occur in Difficult Terrain but instead rarely so if it does then each square or space would cost 15 feet of movement.

Quote from SmiteMakesRight_3_5 >>

The "slope of 20 degrees or more" means that you are moving horizontally on an inclined surface. When the surface is mostly vertical, you are climbing and it is no longer difficult terrain.

 It's also how i interpret it.

If anything climbing up a rope against a wall slope of 90 degree should be easier not harder.