the default skill gain in Skyrim is way too fast and most of the level scaling is balanced around 10-40 and with some pickpocketing and smithing you are able to reach lvl40 that without even completing a single faction or story quest line and enemies start getting stronger too soon (higher levels, better equipment).
So basicly there are 2 kinds of mods:
1. The ones that modifiy the speed at which you gain skill points (e.g. Slower Skill Gain). Means when in vanilla you need 20 hits with your sword to level up, now you need 40. Which means you you gain levels and perks the same way like in vanilla, you just have to do more (kill more enemies, craft more, etc) to reach the same level. You get less xp per action. Their advantage is, you can remove them and your character is fine (just the stuff you explored is more) if you don't like them.
2. And then there are mods which alter the level curve, the skill xp needed to increase the character level. An example for the mod here http://skyrim.nexusmods.com/downloads/file.php?id=2639
The vanilla formula for the xp needed to increase to the next level is Current level * 25 + 75. Those mods alter those values to level * 24 + 116 or level * 20 + 280 and so on which means you need more skill level increases to increase your character level by one at the beginning and less at the end. The "end" differs from mod to mod, the one I linked has the same max lvl of 81 (others change this to 100, means more perks).
Their disadvantage is, your skills level the same way like in vanilla, but you get less level increases meaning less perk points. And when you uninstall them, it might screw up your chars skill/level progress.
Which mod(s) are you using? 1st or 2nd method or both?
I found a lot of mods which use the 1st method and divide all values by 2, 3, 4, etc but no mod that individually adjusts the speed (e.g. reduce pickpocketing, increase alchemy), are there none around?