Most comments on here are about the sparging techniques, I agree your grains are sucking up the sugars. I operate about 72% efficiency but my setup is different. You need to use enough water to cover your grains, let that soak for 60 min, drain, then use the remaining water necessary for your post boil quantity and rinse the grains again for 10-20 min at 160F your malt has gained as much sugars as it can by its first 60 min, anything much longer is going to give off flavors, it requires the rinse of fresh water to gain the needed missing percentage. Fyi, my 5 gallon finish batches start out around 7.5gal pre sparge. Depending on my grain weight, for me it's about 1.8-1.9 gal per pound of grain. And your sparge Temps matter significantly if your trying for a certain mouth feel. A medium body will be about 157-163, higher or lower gets you lighter or heavier body.
Also, calculate your temperatures to off set each other. By this I mean if your brewing in your garage at 50° your grain temp will be about that unless you had a warm storage area, you will have immediate heat transfer from hot water to warmish water when your temperature variance is 100° (grain 60, water 160, the Temps will. Meat somewhere in the middle, about 130, that's to low) so do things like pre heat your cooler while your water heats up with hot hot tap water for 30 min, add your water Temps at 180-185 for cold grains, or try to keep your grains warmer. Ultimately getting that water to malt in 60 min with minimum temperature fluctuations, and a second rinse will increase your % greatly. And cooling it faster. Wart chiller dude, wart chiller. You can diy from copper and hose fitting for less than $65. Happy brewing.