The amount of fluild the GTO manual transmission requires was a big issue that went round and round back in late 2004 and early 2005. The GTO M6 takes 4.6 quarts of fluid. How much drained out of yours is not realavant. If you jacked the car up on the driver's side only and used the fill plug, you still have to measure the amount of fluid inserted just like you would if you filled it from the back-up switch on the passenger side with the car level. If you refilled the tranny with 4.6 quarts (plus or minus a couple ounces) you will be fine.
05 Brakes w/ C5Pads, K&N CAI, TBCoolantByPass, -CAGS, , +Outlets, DeadPedal, UnSpoiled, GasCapHook, PedalsRightSideUp, HitchToGo,