I leveled the carriage and then leveled the bed. I started a print and it acted exactly like the bed was not level. Checked the carriage - it was off level by a half bubble. Re-leveled the carriage, releveled the bed. Checked the carriage again for giggles - of by nearly a half bubble again. I did the lather, rinse, repeat shuffle a couple more times and then gave up. The carriage seems to be going out of level within 5 minutes. I made sure that the threaded rods are tightly attached to the motor coupling, and the couplings to the motors

I cannot see either motor moving to rack the carriage out of level. The one constant is that the left side (facing from the front) of the carriage is always lower when I recheck the carriage level.