my OG with a 75% efficiency should have been 1.079...
(12lbs 2-row, 2.5 lbs specialties) I mash in an igloo cooler with a 1.5 qt/lb water:grain ratio. This time, that ratio was even a bit higher...I had to add a little more than a galolon of boiling to the mash, so my ratio was closer to 1.94.
I collected my first runnings, and let them cool while I was lautering. At 90°F, the gravity was 1.050. In my mind, my first runnings should have been over 1.080.
Ignore the sparge, for now, you could screw around a lot with how fast you add or drain, what volumes you use, what type of manifold you have, or how long you let the sparge water sit, and you might see a few points improvement, but you would be chasing the wrong problem. What you have is partially a math problem, but primarily a conversion problem.
First off, if you mashed 14.5# of grain with ~7 gallons, you might expect a first running gravity of 1.065 with 100% conversion, not "over 1.080". Assuming that you had good mixing during your vorlauf, at 1.050 you probably had about 75% conversion.
Secondly, this was probably never going to be more than 5.5 gallons of a 1.067 beer, if everything had gone well and you got 100% conversion and the ~80% overall mash efficiency expected for a beer of this size.
Finally, with your 75% conversion and a quart of dead space, you would expect 1.036 at 8.5 gallons in the kettle. You got 1.035, so you probably had 95-100% lauter efficiency.
Instead of following a list of random suggestions, some of which would be used to fix problems you don't have, analyze your system like this and you can identify where your problem lies. If you don't measure basic elements of your process properly, like conversion and lauter efficiency, you'll waste a lot of time making random changes instead of informed decisions.
In your case, focus on things that will improve conversion. Crush is most important, then comes pH and mash schedule. Optimized crush, could easily gain you 10%+ conversion.
I've never used those pH strips, so I can't say if they are accurate or not. If your pH is really 6.0, though, you need to get it down, because that is high enough to have an effect on your efficiency. Probably closer to a 5% hit than the 25% that you are seeing, though.
I'd try an alpha amylase rest, too. Mash at your usual temperature, say 152F, for a half hour or so, then infuse enough hot water to bring the temperature up around 158-162F and thin your mash out to ~1.7 qt/#. Some brewers can gain 10%+ conversion efficiency with this change.
According to Kai's formulas, I had a conversion efficiency of 99%, but I'm not sure I understand how that could be possible. Does his table assume qts of water per pound of base malt? or the entire grain bill?
You need to include the entire grain bill for Kai's table to work. Specialty malts contribute nearly as much to gravity as base malts, and Kai's chart is assuming a recipe with a somewhat average mix of grains.