Firstly, few steps of correcting your mistakes which may make you to "feel" Unholy.
You must have 8% hit, it may be more, but non the less-that's not for you, but for your pet's expertise. The expertise on your hero, however, should not be capped and should be forged down, you're not frost DK and you're not loosing much around loosing 1 GCD.
Reforge yourself to hit8%>haste>crit,
then read Magdalena's topic about UDK and fix other mistakes, then you may feel the Udk's gameplay.

In short stick-UDK+Gurthalak>Fdk without 1600-1700 haste(well, that were my thoughts when I played frost for 2 patches)

Gurth always beats Ataraxis for 2h frost, but I'd recommend going dualwield frost with the 2 LFR souldrinkers.

I noticed you're specced 7/1/33, I wouldn't really recommend this spec as a base-spec, since I feel that AMZ and a stronger AMS is much more useful on lots of fights. I'd be more inclined to have a spec that lost outbreak in favor of picking up IBT (since there are more fights than don't use pestilence than don't use AMZ and AMS).

Well to start off with, your kill time is fairly quick at 3:40 which is actually a difficult time for DKs since you're not going to be able to get a second Unholy Frenzy or two good gargoyles in that time frame.

To compare to your logs I found a 25H kill with two good DKs (both pulling in the top 200) with a kill time of only 1 second shorter than yours which you can find here: World of Logs - Real Time Raid Analysis

Lets start off with your cooldown usage:
1 UHF
2 Gargoyles, but the second was cut short
104 RP from AMS
4 uses of Dark Transformation

I also see that you went into Blood Presence - there's no reason to do that, you can soak Hour of Twilight with only AMZ/IBF at 25% nerf. (300 * .75 = 240 * .8 = 192, AMZ is roughly 60k absorb = 132, well below even our unbuffed HP - if you have to soak again before IBF is off (3 minutes) CD ask your raid leader for a pain sup, hand of sac, rallying cry or power word barrier)

With the speed you're killing the boss, you're only going to get 1 UHF, so that's fine. You could find a way to pop out your gargoyle a bit faster, but considering creche is more likely to line up with the first you're probably better off making your first one as good as possible. Remember to wait for an FC proc, a creche proc, and 10 stacks on your trinket, but to still get it out before your pre-pot ends.

104 RP from AMS is extremely low. You can get more RP from AMS in one use (and you almost always will if you use it properly). You also only used it 3 times which is low.

You're generally going to want to be using it 2-3 seconds after every HoT (there's a small delay after every HoT before strikes start again). You will generally try to make that line up with the end of your pet also, since AMS is an easy way to get to 5 stacks again quickly. During AMS you're going to be capping your RP every few seconds (usually for the next 3 hits), so you're generally going to spam DC during that until you get 2 or 3 procs of Runic Corruption, at that point, then you're usually going to end up doing about 3 SS to 1 DC for a next few seconds since avoiding capping runes is more important than avoiding capping RP (SS hits for roughly 1.75 times what DC does).

I already sort of went over this, but you'll probably want to try to get a 5th pet transform in. Usually it will take you around 15 seconds to reload your pet to 5 stacks so you can somewhat line it up with AMS. The first one usually takes the longest if you don't use the 2pc T11 trick, since you're having to use the RP on your gargoyle early on, but you still want to get it out ASAP.

As for the basic rotation, I usually think of it like a pendulum except you're trying to push the pendulum and keep it as close to the middle as possible. The two ends of the pendulum are RP cap and rune cap and since using RP gets you RC procs which give you runes and runes give you RP the two are directly related. I'd definitely recommend not using CLCDK since our priority system is in most cases quite simple anyway. A fairly rough approximation of my rotation is as follows:

If you're at 5 stacks, use Dark Transformation.
If it's off CD use DnD (not on Ultrax though since it doesn't affect him)
If your unholy or death runes are near capping use SS.
If your blood/frost runes are near capping use FS.
If your RP is near capping (20 from the cap), use DC.
Otherwise, SS > DC > FS.

There are a lot of cases in specific encounters that tell me to use things differently, but these are some fairly good basic guidelines until you get more of a feel for the rotation.

SimC also can plot dps result for changes in haste vs. Changes in mastery. I don't remember the tab name, but it is two tabs away from the stat weights. Just select mastery and haste, make 500 point range with 50 point iterations and it will make a plot.