Kyyu sent me 2 of his HDPE nuts to try out. THey were drilled/tapped for 3/8-12 Acme rod. When I first got them I chucked the rod in a drill and ran the HDPE nuts back and forth. At first they were kinda tight, but after a few runs things freed up quite a bit. I was able to flick the nut and it would spin 4 or 5 revolutions.
After taking the YZ gantry out a simple tap freed the existing all thread nut. I touched up the area with a Dremel to make sure it was nice and flat. I then drilled out the existing hole in the ZY gantry a bit over sized.
I took the HDPE nuts, and drilled for 6/32 bolts including through the ZY gantry. Then I took the HDPE nut, and drilled the holes over sized to allow it to float up/down, left/right.
After putting it all back together I moved the gantry towards the motor, and tightened the HDPE nut down, letting it find it's own center.
I cut the Acme rod a little long, and drilled a hole in the outer cabinet piece to allow the rod to stick out a little. I then added 2 Acme nuts as a handle so I can hand wind the Y axis ( I forget where I read about that one, so thanks to who ever mentioned that)

Before I was able to get a good 12IPM on the Y axis. Now I can get 40...well after a few passes of the axis.
Not sure why, but unless I run the Y axis back and forth a few times, it will skip steps only when going slow as when cutting a curved part. When only the Y is running it doesn't skip. But if I run the Y back and forth, then run a cut file, all is well at 40. I am guessing it has something to do with temperature as my basement is rather cool now. If I run the first file at 35, then I can run the next one at 40.
I am using the hose coupler, and no matter what I try it has some wobble. I even heated it as someone here suggested in another thread. I can live with 40 for now, but may get a rigid coupler later.
So THANKS to KYYU for letting me try his HDPE nut. All I did was add that and switch to an Acme rod, and went from a solid 12 ipm to a solid 40 ipm ( well after a few runs up and down the Y axis first), or a little more than 3 times as fast. This is using the stock stepper. Attached files

 

Dorsal... I guess I called them the wrong thing... I was actually looking at 6410K54 and this one 6183K2 in case I didn't get very much improvement or the hose didn't work.
How do you think 6183K2 would hold up? Allows for more misalignment, but I'm afraid it would allow the shaft to wobble.

Like I said I'm happy with it now, and may spring for the coupler at a later date. I'd like to keep it as stock as I can in keeping with the spirit of the design