A couple things come to mind for me that boosted my efficiency;
What kind of heat loss are you experiencing in your mash?
Why use such a big cooler for 5 gallon batches? My 6 gallon batches in high OG brews only need 40 qt tun. That's a lot of head space to lose heat to. I'm staunch in my belief that temperature control in the mash is dang near as important as temperature control in fermentation if you want consistency in your OG for the same recipes.
I never stir during the mash...only at mash in and mash out. I have a form of fly sparge.....it's a plexiglass plate that sits in the cooler lip for the top and has lots and lots of little holes in it (took about an hour to drill them all
). I gravity drain sparge water on the plate through a tube with more holes in it at the same rate as I empty the tun. That helped my efficiency.
You could ask your grain grinder to make a couple different grinds for the same recipes and see how that works. A bit time consuming but it would tell you if the grist is right or not.
I've used both manifolds and ss braids. Seems to me the manifolds have a larger effect depending upon the layout and such. I tinkered around with designs so much trying to improve that I quit and went to the SS braid no matter which tun I use just for convenience and predictability sake.
And I do put my mash tun on an incline even though my outlets are the kind that are in the indented drain....because I want every last drop I can get.