I think it is likely that your settings are too tight. Four washers is about the recommended starting point but one hole at the bottom is not the recommended starting point for the L-brackets. My instruction manual for installation recommends to start at the 5th hole from the top and that leaves four or five at the bottom. Leaving one hole is about the equivalent of adding four more washers.
I don't think you can measure tongue weight the way you did. I think you need to use the bathroom scale and lever method or place the tongue directly on the commercial scale. Perhaps someone with a better grasp statics will correct me.
You can download the Equalizer installation manual that will lead you through the process.
