I think it was the limited edition GNX that would do the 60 in under 5 well closer to under 6 but still way fast for a 80s era rear drive 3000 plus pound car powered by a turbo V6. the GNX had a better intercooler and i think a better turbo. it also had a bar that ran from along the driveshaft an connected to the rear axle similar set up to the 4th gen V8 powered F cars. they also had 16" wheels over the Grand National's 15" wheels and they had fender flares to accomdate the wider wheel/tires and vents on the front fender to let the heat escape from that now almost 300hp V6!.
more can be found about the GNX here
