None of the other Shout mods on the site made any modifications to the Dawnguard Shouts without also modifying vanilla shouts. This proved a problem to me, as I was already using IDS and Ruminations on the Rotmulaag, and didn't want to mess with the alterations from those mods.

So I made this mod, which alters the strength and cooldowns of the shouts Drain Vitality, Soul Tear, and Summon Durnehviir. I've done what I can to keep the shouts as balanced as can be, while keeping them powerful. Note that I use a lot of other mods that increase enemy strength, such as Deadly Dragons, so I'm scaling for those.

Drain Vitality has had its cooldowns changed to 30/40/50 seconds from 30/60/90 seconds. The drained Stamina, Magicka, and Health per second has been changed to 15/sec from 5/sec, but the duration was reduced to 20 seconds from 30 seconds. (This damage was scaled in relation to the Improved Dragon Shouts mod.)

(If you continue to run into the Marked For Death glitch, download the Unofficial Dawnguard patch: http://skyrim.nexusmods.com/mods/23491)

Soul Tear had its 3rd word's cooldown reduced to 60 seconds from 90 seconds, and the amount of health drained was increased to 500 from 300.

Summon Durnehviir had its cooldown reduced from 5 minutes to 3 minutes.

This is the first mod I've put up on the site, so please judge accordingly. Feel free to edit this as you wish.

Recommended Mods
Improved Dragon Shouts: http://skyrim.nexusmods.com/mods/14353
Ruminations on the Rotmulaag: http://skyrim.nexusmods.com/mods/9749
DragonFire - Tactically Enhanced Breath Shouts: http://skyrim.nexusmods.com/mods/18738