Regarding stub axle play.....
Look at your hex pins. Not all of them go through to the other side and secure.
Brand new I swapped out stock hexes for brass ones and reused stock pins.
A 3 months later (maybe....something like that) I noticed some bad play with the stub shaft.
Tore everything apart and noticed some “odd” oblonging of the hex pin holes in the stub shafts.
At first I thought the hex pins had broke on the non threaded end because they were not all the way into the hole in the stub. Only one side was secured.
Ordered up new hexes/pins and some vanquish trx4 stubs.
The new pins are on the right.
The new pins go into the other side of the stub so it is supported on both sides. The stock did not.
Tightened everything up pretty good. Very minimal play.
Something to check out/consider.
ETA - I saw both your post about the slipping and I’ll put my thoughts here.
Are your portal gears stock traxxas or aftermarket.
I’m thinking if they are aftermarket, they may not be meshing well with the traxxas upgraded axles.
If the portal gears are traxxas then something is not right with the upgraded axles.
I’d put back in what works now for the moment and investigate when you have the time.
Just spitballing here.
Good luck. I’ve run into issues as well were my ideas don’t plan out. [emoji23] A lot actually.
Part of the fun.