I'm a level 43 DK too and I haven't had any problem tanking with 1h + shield. I haven't been in Berranid Hills yet but we did whole Dargun's Tomb and some Vol Tuniel and Thelaseen.
The only problem I have is when my group mates (especially the other DK or Sorcerer) get some nasty crits (or I miss a few times) in the beginning. Otherwise I really don't have any problem keeping aggro. Of course ppl have to know how to play and don't go all out right from the pull.
On the other hand, tanking IS challenging. You really have to concetrate on what you are doing to be able to keep enough aggro. I usually pull with Torture and use Provoke when the mob comes. I also use Provoke and Vengeance whenever its up, keep Torture on the mob and when I feel I'm starting to lose aggro I go for Incite - Inflame instead of typical Wrack - Ruin. Black Wind can help a lot too unless you hit some mezzed mobs with it
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