I am no expert, but for pre-fermentation gravity readings use a refractometer they are worth the 25 dollar investment. Much easier to read and it only takes a couple drops of wort.
You might be trying to cram too much grain in your pot and not getting good circulation around your grain. Maybe try a partial mash...or heck just go all extract.
If you have an oven big enough use it to help maintain your mash temp...set in on 150 or so.
You said you sparge quickly? Am I reading that wrong? Sparging should be done very slowly from what I understand.
...that's all this novice has for advise. And for the record I have not yet done an all grain yet. to take all that for what its worth.