1. That cooler tun is really cool.
2. Not sure if this really applies, but I direct-fire my mashtun, recirculate with a March pump via a Blichmann Autosparge and batch sparge (usually 2 run-offs of near equal volume). I am pretty happy all the way around with my results and typically run about at 80% efficiency.
I have found that my mash tun will hold temperature very steady at the front where I have a 1/2" NPT thermometer mounted, but will lose temp near the back when I spot check the mash. I THINK my front thermometer is the best reading and believe something in my process (removing the lid to check temp or something) is to blame for the difference which can be upwards of 10F at times.
Below is a pic of my current set-up. (Boil Kettle, Mash Tun, HLT)