So right after you reset AVG MPG, it's going to behave like instantaneous MPG for a while until you get some miles on it, which seems like what happened. I reset everything each fillup myself.

Higher tire pressures generally help mileage on any car. But the tradeoff is possibly premature tire wear in the middle portion of the tread, and premature replacement. Some tires handle that just fine, since the shoulders usually wear first anyway. Others with asymmetric patterns, like the Goodyear Assurance TripleTread, need to be kept close to the car's spec'ed pressures to achieve anywhere close to their rated tread life, based on my experience with this particular tire.

Another thought is your 4WD Transfer case and driveshaft to the front diff may have contributed to your clunk. Your trans is probably fine. Between two driveshafts, two diffs, a 2 speed t-case, no torque converter (just a spring-loaded damper), on top of a trans with two heavy electric motors, I'm actually surprised you don't have more stuff like this. That's a lot of spinning parts and inertia to manage in one drivetrain.

 

Just a data point. Driving the kids to school, three miles into it, bumper to bumper and the engine was still running. I clicked over to trans temp and it said 79 degrees and it was 51 degrees OAT. I commented to my wife how we were discussing this issue, and the engine switched to auto stop about another 50' down the road. Trans temp was 82 degrees when that happened. Engine temp gauge was a little above 1/4 scale when the trans was at 79 degrees and only a little higher when it A-stopped.

 

I was in ICT for the week and left the Tahoe outside rather than in the hangar, a little bit of a rush to leave not good. The Tahoe experienced temperatures of -5 to -8F. When I returned it seemed as though for the first few hours it ran a little rough. Also the transmission clunked a little going from forward to reverse, like you experienced Mel. The following day which is today everything is normal. Outside OAT -9F.