I get anywhere around 78-82% attenuation when I use US05. I think that the water could definitely make a difference and I'm sure some others will chime in that are more experts in water than myself. What about aeration of your wort, have you changed anything with this?
I've had the same problem with Wyeast 1214 and I don't use it anymore. However, one did get better with age, but I just don't have the patience for that. I do like Wyeast 1762 (Belgian Abbey II) much better (less estery) and I start it in the low 60's.