I think when you move a node, the nodes adjacent to it have their slopes adjusted accordingly. So if you have a node that you've just moved and you think its slope should be recalculated, try moving an adjacent node slightly (and then you can move it right back) and the node you're concerned about should fix itself.

If it still doesn't have the slope you want, the Node Controller mod can make manual adjustments to node slopes (and other aspects of geometry).