Actually, it seems that the main problem you're having is due to those motors, which have extremely high inductance and low current: https://www.applied-motion.com/produ...otors/ht23-399 . I'd be happy to sell you a new CNC-ready Taig, but it wouldn't make your problems go away if you just put those motors and that same motion-control system on it. Your money would be much better spent in buying different motors (like these, for instance: 23HS7430 1.8 Degree 3A 2.4V 2.3mH 150N.cm Brushless Stepping Motor for CNC - Free Shipping - ThanksBuyer ), another controller, like the Geckodrives G-540 and a 48v 10 amp power supply. Altogether, this will cost a lot less than you're planning to spend, and you'll be amazed at the difference; it should go at least 3 times faster without losing steps.
If your mill is really a Taig, then it has 1/2" diameter screws, not 1/4". The weight of the motor isn't the issue; your machine has a lighter motor than the one that comes standard on the CNC version (you could think about upgrading to that one), and the mechanical advantage of those 20-pitch screws is eminently capable of raising it without losing steps. Just get rid of those crappy steppers and don't look back...