Yes, the Lyman 55 should be throwing more consistent than that. I don't know anything about Clays, so I can't comment there, but nearly all postol powders exceppt Unique have always metered well in all 3 powder measures that I use, including the 55. Trail Boss is a little bit different than other pistol powders though. I know that the Lyman instructions tell you to only use the top slide for pistol powders. In spite of that, try using the middle slide for Trail Boss. With all 3 slides starting at 0, try pulling the middle slide out a little ways. By trial and error, get it set until it is just slightly below or right at the desired weight. Adjust the top slide just a smidgen if needed to get it perfect. That will work much better than just the top slide for Trail Boss, and a few others as well.
Make darn sure that you have the lock screws clamped down tight after you make an adjustment of course. They can be a little loose and you slides change just a little bit.
Also, make sure that when you raise the lever to the "up" position, that you puse for a second, then use the "tapper" once or twice to let it settle. Sometimes it takes throwing 10 charges or so before things kind of settle down for a given adjustment.