Question...My understanding is that unless you bought a GT2, all 2018 GTs had a peg leg rear diff (one wheel provides traction). How is it that I just laid 2 tracks?
Both an open differential (peg leg diff) and an LSD Power both rear wheels.
The difference is that when one rear wheel spins faster than the other, the LSD will lock and both wheels will get a similar amount of power. So you see two spin marks at most times when there is wheelspin.
An open differential will also make two spin marks as long as the rear tires have similar traction on both sides of the car. However, if one rear wheel has significantly less traction than the other, the wheel with less traction will receive more of the power distribution than the wheel with traction. That leads to the low traction wheel spinning/slipping (leaving a mark on the pavement) and the high traction wheel relatively unpowered and just along for the ride (leaving no mark).
Just remember that regular diffs power both wheels evenly until one starts spinning faster than the other, then that faster spinning wheel receives an ever increasing amount of the rear ends power.
LSD addresses this by mechanically locking the wheels together in situations where one wheel might spin faster than the other.