If your blades are recently sharpened and you are still getting burning, the carbide tips are probably too far gone. Another possibility is that the sharpening was not done properly and they need to be reset. The most likely cause is it is just time to replace the blade. It is less likely that the blade is out of square, since your corners would be off as well as burned.
I have very good luck with Forrest blades. They literally can last a lifetime of continuous use if they are sent back to Forrest for sharpening and reconditioning. They are actually less expensive than the local guy, and the blades come back perfect every time. I don't even know how old my chop blades are since they were on my used Pistorius when I bought it.
They are very good to talk with you explaining the technical aspects of the blades, even blades that are not theirs. I recently bought a new blade for my table saw and found them to be very helpful.