I'll try to respond to several things at once here...
* Thanks for the tip on more water in the mash/sparging process. I knew that was going to be a problem going into it. I had anticipated 65%, but landed with 57%... lower than expected. The problem is that I only have an 8 gallon brew kettle, so 6.8 gallons is pretty much the max I can fit in while boiling. More water wouldn't have helped, although a better quantity balance between the two mashes would have been a good idea.. I suppose I could split the 1st runnings and second runnings into two separate kettles... hmmm.
* my boil-off rate is pretty low (.56 gal/hr) because my stove sucks. I boiled from 6.8 down to 5.5 gal over the course of a 140 min boil. It's about 10d outside right now in MN, but I have a propane burner ready to go come March.
* The efficiency ratings I was quoting are based on a different definition on assumptions, I think. I calculated the potential gravity from the grains mashed (~755 gp) and compared it to how much I was able to extract (~421 gp). There's my 57% eff from my mash.
* In the end, I'm not as concerned about the mash efficiency because I can attribute this to me being a rookie with AG and the fact that I was mashing a huge amount of grain for only a 5.5 gal batch. I think this will improve naturally over time.
* As for the gravity bump I was expecting from the 1.5 lbs of extra light DME and 6.2oz molasses... the sources I have cite the DME to be 44gp/gal (equiv. of 12 gp for a 5.5 gal batch) and molasses (equiv. of 2.5 gp). I guess I was off a little, but still... that should have bumped my 1.077 post-mash gravity up to 1.0915... not just 1.083... right?