87 was last year for the GN, 88 was last year for the SS.
You'll probably have better luck with the CZ code SS Monte core.
CR & KC code cores are good to work with also. Jakeshoe has experience with them, tuning them for higher rpm auto shifts using the CZ/SS code Governor. I think he said with CZ Gov, they shift around 6100-6200rpm.
The GN's BR/BQ codes seem to work best with the lower rpm turbo V6 engine from what I've read.