Userform slow to enter data - event handling issue (I think)

I'm not smart enough to get to the root of this myself. I'm fairly certain this an event handling issue and I need to suppress events as part of my userform, and I've read http://www.cpearson.com/Excel/SuppressChangeInForms.htm, but I can't figure out how to apply that solution to my sheet.

All three of my userforms in the attached sheet are frankly quite slow. I'm pretty sure this has to do with my use of dynamic named ranges in populating the drop-downs in the combo-boxes, but again I can't figure out how to avoid this slowing the form down to a crawl when hitting submit.