I also had low speed lean burn problems, and occasional but repeating CEL's re. the EGR. Things have been much better since Jan. 17; read below.
Try Marvel Mystery Oil (MMO) in your fuel, 4 oz per 10 gallons of gas, per the bottle instructions. And 10% of sump capacity in your oil (MMO bottle says 20% but I used 10%). I think it's the MMO in the gas that does the trick, for my car anyway.
Till this past January, my HX would only allow lean burn down to about 61mph. It was that way for over 3 years / 70K miles, including after I had the head rebuilt professionally. Occasionally I'd see LB between 46-61 mph but sometimes only a few seconds, sometimes a few miles. Then no more. But other Honda lean burn drivers reported LB down to about 45ish mph. I found it frustrating.
One day this winter I added MMO as above, in the sump and the tank. Boom! Lean burn came back. Now it holds LB down to about 45-46 mph, as long as I pay attention to the amount of MMO in the fuel.
Then I refilled the tank and didn't think to add MMO with the new fuel. Low speed lean burn went away. Pulled over, added it, low speed LB came back. I've had good results using between 2-4 oz per 10 gal gas. I'm tending towards 3 or 4 oz but I haven't completely settled my scheme yet.
My current tank isn't visible in the gas log yet. Low speed LB is working again, and my nice LRR Michelin snow tires are back on the car, and MPG is back up around 52-53 so far for the tank.
Working this since Jan, I've seen low speed LB go away about 2/3 way through the tank. Deduced that MMO is heavier than gasoline, is gradually settling to bottom of tank and gets sucked up by fuel pump. Gradually reduces the concentration. I'm testing adding an ounce or so about half way through the tank to compensate.
See my gas log. See notes on low speed lean burn for the Jan. 17 and Jan. 27 2012 fillups.
You'll need a funnel with about 10-12 inches of hose or tubing. And a rag to wipe the funnel.