SharBear,
I admire your persistance thus far. There are really two keys for precise blocks, and cutting is the first.
The second key is the accurate 1/4 inch seam. I struggled for years with my blocks and didn't know why. I cut perfectly. I had a 1/4 inch foot on my machine. Blocks were not right and I redid each one several times. Then one day, I measured my seams. They were too big. It occurred to me (by reading my owners manual for the machine thoroughly, and by reading a few magazines) that there was a way to move my needle over two clicks to the right. This realization, in conjunction with my 1/4 inch foot (which only guides the material along) has made the whole difference.
Before you throw in the towel, try this: sew two strips of fabric together. Say your strips are cut perfectly at 2.5" x 6". Sew them together along the long side. Open, and press, then measure the width of the two strips together. The width should be 4.5". If not, then see if you can adjust your needle position.
PS
I also love the applied math aspect of quilting.
Good luck.