I had this problem too after attaching the spindle mount and corrected it by adding a washer to each v-wheel shaft on the carriage. This moved the carriage away from the vertical maker rail slightly and stopped the acme rod from binding in the delrin nut near the top of the carriage travel. I had a bit of wobble in my acme rod as well but don’t believe it to have been the cause of the binding.
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Fixed my issue. ACME rod is bent slightly, but not enough to be the problem. I had added a washer to each v-wheel assembly to move my spindle carriage out from my Z-Axis far enough that I didn’t have to sand down the edge of my Dewalt. This was causing the rod to bind as the carriage approached the top of my Z axis. A spacer between the carriage and Delrin nut fixed my problem. The M5 washers that I used on the V-wheels were too thick, but a business card cut into 3 layers thick did the trick.
It is worth taking some time to work the parts of this section of the install. Thank you to all the prior comments as this was an issue with my rod as well.