If I had to guess, it would be the different math you are subject to at 85 than you were earlier. The biggest thing I remember with my shaman when it hit 85 was the dramatic drop in hit. It went from excessive to almost none. Same with haste and crit. She still doesn't have the same dps at 85 in better gear than she did at 84.

She went from the ability to hit anything and a 30% some odd crit rate to 15% miss rate on level 82 and higher mobs and a 6% crit rate. I might be exaggerating a bit, but I really remember dinging 85 and everything became insanely harder, even just questing.