Ok, I had several highway runs over the weekend, and I have more stuff to report. If I was in 3rd or 4th gear turning on the a/c did not increase my load, and my instant MPG remained the same. A/c on did ding me when I tried p&g though. P&G, 55 mph, windows up, a/c off the SG reported 75-80MPG. The same with a/c on the instant MPG only went to 55-60. I'll probably purchase fuel this evening so I can finish the calibration of the SG, and have the instant MPG readings more accurate.
Well, I purchased fuel last night and set the calibration on the SG. Turns out that it wasn't that far off to begin with. The variance was only 1.4% or something like that. I hypermiled like mad (mostly p&g, kept speed under 55 unless gravity took me faster) on the way home, but it still reported about 4 MPG less on the trip than I've done on the exact same route, under the exact same traffic conditions as before. I think this is because there is still 8-10 oz of methanol in the tank by my estimation. That first methanol tank really dinged me.
I noticed in one case I was drafting behind a dump truck @ 60 MPH. The draft was so good that I was actually idling faster than he was going so I had to back off some more.