No matter what I do when making stacked tiers, they end up unlevel. Ugh! I level each layer prior to icing. I have each layer on their own board and ice them. Using precut dowels (I like the hollow cardboard dowels) put them in the bottom layers (minimum of 4 dowels, more for bigger ones). But it never fails, when I get all layers stacked, it is crooked. What am I doing wrong, or not doing at all??? Any and all suggestions are appreciated.

Have you made sure that your work surface is level? If your table/counter is level, and each tier is level and your dowels are all cut evenly, the finished cake should be level also.

I have severe astigmatism and do not see "level" or "plumb" well at all, so I keep a small carpenter's level (bought for this purpose - not DH's dirty used one LOL) handy at all times and check as I build. Checking your work surface is the first in line - my little Wilton turntable is not level.