Use a larger tray (16x20 for 11x14 prints).
Use at least 2 liters of toner in a big tray.
Use a more dilute solution, and tone longer.
Use gold borax.

You know, if the edges of the paper are curling (and I know from experience they do), that could account for your uneven toning. If your solution is strong, it'll only take a few seconds to cause a noticeable difference.