I attempted to install SSD Overdrive gears in my Vanquish D44 axles. They were extremely notchy. I tried shimming the pinion outside the diff case, but it didn't help. I ended up pulling the SSD gears out and swapped in a set of Vanquish gears. The VP gears were smooth as silk in the D44's. I was able to use the SSD overdrive gears in my SSD Trail King axles, where they spun smooth.
I have now built about ten sets of AR44-type geared axles - ranging from stock Axial SCX10 II's, SSD Pro44, Diamond Pro, and Trail King, Vanquish D44, and Axial Capra axles. The first four of so sets of axles I built were all SSD's and the gear sets all had 3-bolt lockers. They all spun smooth with no shimming. But I started to have issues when the switchover to 6-bolt lockers happened. The last six or so sets of axles I've built have all had 6-bolt lockers, and I've had quite a few of them turn out crunchy to locked-up and unusable. Shimming has helped a little on a few of them, but some were so bad that the only thing that has really helped is swapping gear sets around among the axles to find a combination that works.
I'm really finding that only certain gear sets work well in certain axles. There's no clear rhyme or reason to it, but I have found that it can help to use gears made by the same manufacturer who makes the axles, and also to not try using older gearsets in newer axles. But that's not always consistently the case. Maybe I'm just doing it wrong, but I tend to think not. I've heard that Axial changed the design of their axles just a little bit, and while that would explain some of the issues I've had, it doesn't explain it completely.