Be sure the slide pins and their bores in the caliper are very clean and well greased. I was having some brake issues and found a couple of the pins had pretty much frozen in the caliper. I think the last time I replaced pads, I didn't bother cleaning and re-greasing them, and the grease had solidified.
I picked up new o-rings, cleaned everything well (cleaning the bores in the caliper isn't easy, but twisting up a paper towel into a tight spiral and pulling it through works pretty well), re-greased 'em and it was a huge improvement.
