http://www2.nadaguides.com/GlobalFra...el=04000800152
That is for the 1987 GT. There is no technical difference between the 1987 car and the 1988 car.
The 1988 car is listed at 3194lbs, but that could be loaded with an auto, the Coupe only increased in weight 37lbs that year, from 3000, to 3037.