Efficiency Problems. A comedy of errors?

Good day.

I was once an avid homebrewer, and was consistently able to hit my OG without any problems. I used grain milled by BWS. I batch sparged in a cooler with a braid. It was never an issue.

Fast forward 3 years of brewing inactivity. I'm back into it and have done 4 batches with a very uniform 66% brewhouse efficiency. The first two brews were with grain milled by the HBS. The last two were brewed with grain milled by me in my Monster 2.0. I bought the mill hoping to improve efficiency. I'm missing my OG rather consistently by .005 each time (1.064, not 1.069 etc.).

I also have found that my cooler has an odd temperature problem. I preheat my cooler before starting. Then I mash in. After stirring well, I'm seeing anywhere from a 5 - 10* temperature flux between the left end of the cooler and the right end of the cooler...could that really be right? Looks like if stirred well then that should not be an issue, especially in a pre-heated tun.

As for sparging, I split it into two sparges. 185* water. Pour in, stir, let sit for 5 -10, vourlauf, drain. Again, I do this twice.

I'm not sure why I'm not getting better numbers. I hate missing my numbers. The beer tastes fine, but it's a mental thing. I'm not 66% at anything else.

Should I tighten up my mill? It's set at .39. All the kernels are busted. I'm not seeing a ton of flour, and a lot of flour sticks to the side of my bucket. Should I be sweeping that into the mash?

Would the temperature differential have something to do with it? Why is there such a severe difference I wonder?

Am I sparging improperly?

It's just a gigantic gaum at this point. I'm pretty pissed about it and need someone to give me a hug and tell me it will be ok.

Seriously, what am I overlooking? What would be your checklist?

All help is appreciated. I thank you in advance.

We really improved using a HERMS system with a Chinchiiler Cooler but that takes two pumps (One for hot water and one for Wort. We use 10 gal round coolers before we went with a Stout Mash Tun. We could do 15 to 20 gal batches using 2 coolers.

I also go the Brew Math app for my iPhone. It will tell me the water temp before I pour in the grain. I make sure that my mash water is at temp degrees before I add the grain. I used have to add a cup of COLD water to get to temp because I did not trust that the temp from the app was correct and would get it hotter. I now use the exact temp and my Mash is right on. By having the water at the correct temp and volume, I do not worry about the Mash Tun correction as I have taken it out by preheating totally. In fact I normally put the water in about 15 degrees higher and then add cooling water to get to near the temp. I leave on the high side and leave the lid off and wait for the temp to fall to the brewmath temp and then pour in the grain.