Your not doing anything wrong, they just hit hard.... I was just as frustrated when I got there. Pretty much just cleared all Ramparts, BF, Slave Pens and the trash up to 1st boss in UB for xp. Then mixed in some quests to change it up every so often. For me, I felt like there was section of frustration between 63 and 66... Then came the Earth elementals and runs became MUCH smoother...All I can say is grind out all the instances you know you can so you can get to 66 and things get better from there. Just my 2cents