I kinda have the same experience.
Did my first Heroic dungeon yesterday with a guild group, and although I won an item, I could almost cry.
Half of the time I was below the tank, and the elemental shaman did about 1.5-2 times my damage. (he had a lot better gear though, but even then)
Even the shadowpriest, whose ass I normally kick by a fair margin, and who had lesser gear than me, outdps’d me with more than 25%
I was reforged to be hitcapped for heroic dungeons, but the lack of haste really showed. (especially during cleaves, I was kinda dieing inside)
If I had 12 seconds left on SnD or rupture, I had to be careful to have enough combopoints by the time it dropped off. 12s to build 5 frweaking combopoints is kinda ridiculous.
I did at least 50% more DPS at level 85, than what I do now at level 90.
And even if my gear is not up to par yet and largely unenchanted (ilvl 449 atm with 2 ilvl 450 weapons), it is kinda weird to see myself level 5 times, only to see the DPS plummet.
Is a character not supposed to become stronger when they level??
I really hope to see my DPS taking giant leaps every time I get an upgrade, or I will be very pissed at blizzard by the time I step foot into raiding.