update.
So after using over a half tank (well by the gauge) and adjusting the idle up for what will likely be summer "AC Idle" @500 in Drive - I am getting 13 MPG. This is still 80% if not more highway (re: Tx Farm Roads) driving. My 1st outing with the AC was not so happy, I had to keep putting her in neutral, so I upped it. I'd say it's 700~750 in neutral now. This half tank also wasn't me trying to get the best possible MPG. I wasn't dogging it all the time but I was far from being a grandpa too. Nothing like going WOT to beat a few yellow lights or passing some slow poke ;-)
I guess that is good?
PS: Last night on our drive I actually ended up being behind a 68 or so C10 on the
Devil's Backbone Scenic Drive. He was very low to the ground and was either a dark blue or perhaps even purple - I couldn't tell as it was dark. Though I could tell he had the same LED backlights as me! I was really hoping he was going to stop at the bar or the rest stop but turned on a secondary road. I thought it would be weird if I had followed him to a house LOL