recently i attempted to build the newest URSA Bear truck and ran into a big issue with the gear mesh in the new GB03 axles. no idea why but the gears are skipping where before they were not. So i just made a slightly larger Diff gear to close up the mesh between the upper counter gear and the diff without modifying the axle case or anything else.
the stock Ursa gear is 28T, this new gear has 29T so it slightly drops the gear ratio of the axles as well.
this is just a quick fix so it might lightly touch on the inside of the axle case but it will wear away just a little and break itself in.
i tested this on the bench and a few minutes on the floor under some load and it did not skip or pop but your mileage may vary. try it out hope it works for you.