try to mash in at the same temp, dont mash out and mash for only for 45 mins- 1 hr for higher gravity beers. recirculate it (if you do) and start to heat it in the kettle.
the reason your temp drops durring sparge is because the pt100 isnt getting circulation, completely normal to see.
2.5 hours is very long for a mash...... the longer you mash the more the enzymes cut up the sugar chains which in turn make a very fermentable wort.
and dont worry about the raters...