Shenlonco:

Hmm I think it shouldn't be one motor getting more electric than the other because the tank move forward/backward in a straight line regardless of what speed it was running on initially for the 1st 10 minutes (unless the electric distribution changes after 10 minutes)

When the tank starts to veer/pull to one side, this will only happen when I'm using maximum speed (push the forward/backward speed to maximum top/bottom position)

At the distributor testing platform, when the tank starts to veer, it will veer left when going forward in max speed and veer right when going backward in max speed (assume X, Y coordinate is [100,100] in pixel mode like paintbrush, moving forward land in [75, 0] while moving backward land in [125, 200])

The distributor tries to put 2 circle sticker on each track of the same vertical position and after running for 3 seconds, the circle sticker have run out of alignment with each other

I have suggest the motor break-in as one of the cause to the distributor so that he have information to discuss with VSTANK.
I probably will give him this forum URL for additional information.