Short answer: I don't know of any such mod, although there are a few that deal with climbing. Maybe check mod categories, or enter "climb" to the nexus file search bar or "skyrim special edition climb" to a widenet search.
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What is the "pg"?
As for change in movement speed on hills, I've only noticed it when climbing difficult mountain faces or slides (those almost smooth faced hills that are well above 45 degree inclines?, (I think they're meant to model mud/moss slicks and other soft soils) and that is, afaik slippage (via gravity) rather than some speed-reduction trick. (although you might have some such mod installed for all I know)
I don't think it's meant to be "easy" to climb a sheer rock wall. But console TCL always gets around that.
My main working principle when facing a difficult climb is stubborness and persistence... and knowing when to give up and go the long way 
It's also possible that one's level may have some affect on climbing ability, although I can't recall and haven't been low level in a while.