The V6/GT cars for 94-Present use a 10" solid rear rotor and single piston caliper. While they are disc brakes, the non vented rotors are less than optimal. You can upgrade to slotted and drilled rotors from companies like Baer , but the are still solid 10" rotors. Here are your upgrade options beyond just the rotors:
1. Upgrade to a drilled and slotted rear disc, stock size. Baer carries the item
2. Upgrade to the 94-98 Cobra 11.65" vented rotors. You need the Cobra specific axle bracket, anti-moan bracket and rotor. You use your existing caliper with the cobra pads (they are thinner to accommodate the thicker rotor). There are 3 different caliper brackets for the 94+ cars. You can either get a cobra specific unit or grind the GT/V6 one wider to accomodate the wider cobra rotor.