I like to add in nasty traps and hazards to encounters. And ways to disable them of course. It's fine having the base of a module to start with, but then I like to build on that, add a bit more 'fantastic' to the fantasy, let my imagination run wild, make the players sweat for that xp.
How did your players get to level 5 using KotSF? Did you add in lots of side treks? Or did they just clean every nook and cranny of the place? If too much xp is a problem maybe you need to be a little less generous for a while. Don't give xp for traps or hazards for example. Maybe reduce the rewards for the completion of quests. People on the boards often talk about removing xp rewards, simply levelling at appropriate moments of the game (at the DMs discretion). My group doesn't have massive amounts of time to play and they RP a lot (once a week or every two weeks for 3 or 4 hours) ... so I'm happy as mud for them to progess as quickly as possible (I'm dying for them to get to paragon level! Yeah underdark here we come!).
The modules I'm running are a mix of a level 1 module (rescue at rivenroar) and a level 4-6 module (curse of the Kingspire). They are just about to reach level 6. So I just use the story/maps from the level 1 module but I have placed appropriate level monsters adjusting the counter level so they are appropriate/challenging. The Adventure Tools makes this incredibly easy. I want some kind of Eladrin undead ... type in eladrin as a key word, and every eladrin that exists comes up, ohhhh, winter eladrin... very easy to reflavour as undead. Bingo! 2 seconds, literally. Spend up to limit of xp budget (in this case = level or lvl+1 or +2 ... it's a long adventuring day with difficulty to withdraw and rest due to time pressures, so I don't push the difficulty any higher than that.)
To reduce the length of the module I built a skill challenge into the adventure hook that if successful will allow the PCs to wipe out the VAST majority of Hobgoblins on level 1 of the dungeon in one fell sweep. It's great to avoid the battle after battle repetition, and in your case great to reduce the amount of xp the pcs get their grubby hands on: over 20 creatures wiped for the modest price of a complexity 2 level 6 skill challenge!!! Not to mention the time saved (more relevant in my case).
Maybe you could do something similar for the first part of the Thunderspire Labyrinth. Maybe this will give you the spark of a useful idea. My PCs were given a quest by the leader of a rival band of goblins, Sarnossug, who planned to take revenge on the Red Hand, a more powerful band in the area that had subjugated them by force and humillated him personally when he was forced to swear allegiance. He offered them a deadly object, a crystal ball of death, disguised inside a wicker doll, in exchange for leaving him and his goblins in peace to raise their dead master, the Ogreking. The Red Hand were awaiting the delivery of the wicker doll which was supposedly meant to be used in a ritual to raise the Red Hand's legendary leader Rollock the Whip. Their mission to join as many of the Hand together by art of deception (each PC receive a bitter leaf to chew an hour before infiltration, in order to alter their appearance to that of a goblin. The effects lasting 1-2 hours) and then trigger the Ball of Death. The Pcs would then have five minutes to leave the area unnoticed before the mortal explosion of the Crystal Ball of Death. Here's what I did with the Skill Challenge:
Assassinate the Red Hand with the Crystal Ball of Death
Infiltrate the Red Hand and convince them to join together to invoke the spirit of the long dead leader of the Red Hand 'Rollock the Whip'; leave the area inconspicuously before the Crystal Ball of Death explodes
The PCs must chew the Bitter Leaf an hour before they wish to make the change in appearance; Its effects last between 1 and 2 hours.
Level 6 Skill Challenge
Complexity 2 (6 successes before 3 fails)
Primary Skills (Below difficulties are guidelines, see 'Sequence' below)
Bluff (hard)
Diplomacy (hard +2)
Intimidate (hard +2)
Religion (hard +2) Max 1 success
Stealth (Final success must be attained using Stealth; see below)
Secondary Skills
Creative Liscence; (Hard) PCs can be inventive with other skills to aid their primary skill checks. Each PC can attempt this once during the course of the Challenge
Insight (moderate +2)
History (Hard)
Arcana (Hard)
Sequence:
Part 1: Appearances: First visual encounter with the Guards in Area 1. One person leads the Bluff which is only Medium CD 12 but is modified with +2 CD for each PC in group who fails to Bluff (CD 12) [all pcs roll, they have to keep their nerves calm to no give the game away, even if they aren't doing the talking]
Part 2: Meeting the Captain of the Watch; The only one who knows details of the Doll on the 1st level arrives with HGoblins from area 2. Under his inspection all must reroll Bluff CD 12 to determine CD of his questioning; +2 CD for each fail
Question 1: 'The spirit of Rollock the Red Hand, do you have it with you?' Sarnossug lied, telling the PCs it was merely an idol they worshipped. If they are not surprised by the question or affirm it, Captain's suspicion will be aroused, as Sarnossug had promised he would keep it secret: CD Difficult to affirm CD Med to deny.
Question 2: (When Captain sees the doll): 'This does not resemble the most legendary warrior of the Horde, it looks more like a child's doll!!! Your master, rat that he is, does he attempt to cheat us?! CD Difficult + Group Bluff Mod to calm his suspicions
Question 3: (once convinced) 'We are 14, and I am sure you also wish to lend your strength to invoke Rollick, I imagine we are enough? CD Difficult to convince he will need more people/everyone possible; If successful the Rage Drake Guard is also called
Question 4: (passing comment) 'We do not wish to mix the blue bloods in the ritual, so let us prepare.' Chance for the PCs to counter this thought and include Gnomes and Bugbear Assassins
Question 5: And so here we all are ... what now?' The PCs have to convince the Hand to gather close around the doll and occupy them long enough to make their getaway (this will require another check if 5 have not yet been achieved); the trigger word remains Jezuel (Lady X); once said they have 5 minutes to escape!!!! And remain Hidden!!!!
Final Stealth Check:
At least one success must be achieved this way before the end of the skill challenge
All PCs must make a roll, to move away from the area unnoticed before the Crystal Ball explodes; Allow creative use of other skills to provide a bonus to stealth check; +2 bonus is standard but especially clever methods of evasion can be rewarded even more:
4 successes achieves a success
3 successes is neither success nor failure
2 is a failure; The PCs must think fast or be caught in the explosion. All the PCs who failed the Stealth check must improvise with their skills to escape observation and avoid disaster; the amount of successes necessary is as above. However another consecutive failure causes 2 additional failures.
Even if the PCs now achieve a success, any PC who rolled a second failure is partially caught in the blast and loses 2 HSurges
success: The PCs sneak away safely without being noticed
failure: The PCs are spotted acting suspiciously; the Hobgoblins look at them for the first time as if they truly began seeing what was in front of their eyes. The ritual magic of disguise begins to waver; even the wicker voodoo doll begins to flicker and change shape become more rounded and crystal like!
Victory: All Hobgoblins in Areas 1, 2, 3, 8, 9 are killed
Defeat: Tactical encounters 1, 2, 3, and will also trigger 8 and 9 in room 2 simultaneously.
Hopefully this will be useful to you in some way when/if you take a look at Thunderspire module.
