I know keeping shaft end play close to zero makes gear mesh much better for 3rd gear. I have a truck that has been putting some serious abuse to an NV4500 built by me and 10k miles later no issues. Weekly burnouts, launches and towing.
I am considering doing a full cyro trans including case. Also thinking of maybe redesigning the 5th gear synchro hub to have 2x as many spline teeth and machine the end of the mainshaft to match so they do not tear out.