A couple points, right off the top of my head (more may come to me with more thought):
Your strike water volume was a little on the low side. In US units (I'll try to provide metric conversions, but make no promises for my math!), you typically want 1-2qts/lb of grain (if my math is right, that looks like roughly 2-4lt/kg?), and after I double checked your conversions it looks like you have just barely 1. I usually shoot for 1.25qts/lb (2.6lt/kg), which leaves me room to add some boiling water halfway through the mash to boost temperature if I lose any (which definitely happens this time of year in Connecticut!).
As for sparging - I've never heard of sparging with your wort before. The whole idea of sparging is to rinse any residual sugars out of the grain bed that didn't come out when you drained out your first runnings. It's possible (this is a wild guess here, smarter folks than I will probably refute this, and I'd welcome their insight!) that sparging with your wort could actually leave behind some of the sugars that you extracted in your first runnings back in the grain bed. In short, don't do that anymore!
I also notice that your strike volume and your sparge volume only add up to 5 gallons. This is a big reason for your leaving behind sugars in your grain bed - possibly the biggest. I assume you know your boil-off rate from previous extract brews, correct? What you should do, to calculate your sparge volume, is look at the volume you get from your first runnings. That will never equal your strike volume, since your grains absorb a LOT of that water (I forget the exact proportion, but I want to say it's somewhere around 25-35%). Anyway, measure the volume of your first runnings. What you want in your brew kettle is your intended final volume PLUS your boil off amount. So, say you want to wind up with 6 gallons in the kettle (most of us to it that way - figure half a gallon to trub loss, 5.5 gallons into the fermenter), and you know you boil off 1 gallon in an hour (just to make it a round number). That means you need a total of 7 gallons. And say your first runnings leave you with 2 gallons in the kettle. 7 (your intended kettle volume) minus 2 (your first runnings volume) is 5 gallons, which is the volume you should sparge with.
Now, you're still a little hazy on your sparging technique - but I'm going to assume based on your description that you're doing what's called a batch sparge. That's where you drain the mash tun of it's first runnings, then add all the sparge water in one batch (oftentimes broken up into multiple batches), and drain that off again. I almost always break my sparge into two batches. So in the example above, I'd probably split it up evenly into two 2.5 gallon sparges.
Another important element is stirring. You did say you stirred at the beginning of the mash to avoid doughballs, and that's a good thing. But is that the only time you stirred? I typically stir again halfway through the mash, and I always stir during each batch sparge. Stirring during the mash probably isn't strictly necessary, but during a batch sparge it's absolutely crucial in order to get the water evenly distributed and to get the whole grainbed rinsed evenly.
So, I think if you mash with just a little more water, sparge with the right volume of water, and make sure you stir when you sparge, you should see a big improvement.
