I don't believe you can gift a Dk from 55 to 60. When I was playing with mine in beta you couldn't get summoned out of the area, and everything was phased/instanced so you couldn't get next to your DK with a non-DK. And you have to do all the starter quests to get all your talent points so it isn't worth skipping the zone (I don't think you can leave until you've done them all anyway) Now you can certainly gift your DK from 58 to 60 once he's out of the starting zone. I ran the DK starting area twice and both times came out at level 58.5ish.