Jimbo - here is my list of the things to try, in order of importance.
Crush - you have examined that. Maybe post a picture and see what the experts say?
Temperature - check your thermometer. Hitting the right temp(s) is important.
Mash pH - My efficiency improved when I started paying attenetion to mash pH and adjusting. You are doing this already.
Calibration - Check you hydrometer. Should read 1.000 in water.
Volumes - Have you marked your boil vessel for volume? If you do 5 gallons and are off by a quart that is 1 part in 20, or 5%
One thing that we started doing recently is knifing the mash. This technique is something I read about on the HBD back in 90's, and tried for a while back then. My mash technique was not very good back then so I gave it up. When at Sierra Nevada's Ber Camp this was discussed by Scott Jennings, the Head Pilot Brewer, as something that inceases efficiency.
Here is how you "knife" the mash as a homebrewer. Do this when you are about halfway through the sparge. Use a long handled spatula, not a knife. Pull it through the mash, making a grid pattern with aboiut a 1 inch spacing. Stay about 1 inch or more above your false bottom or screen, and your mash will still run clear.
This has improved our effeciency from 80% to 84-85%. Our mill is an unadjustable JSP.