They make custom trans controllers to utilize the internal TCM.
I believe that is also covered on the fiero sites.

The 6T75E is rated about the same torque as a 4T65E-HD, with the main difference being that's in a 5000-6000 lbs SUV; as such the LS2 6T75 has survived in the Fiero attached to a very powerful Fiero just fine.

I think it would make a big difference in drive-ability to be honest - I've always felt that we're missing at least a gear (understanding that 1st gear traction will be difficult).
My 1st gear goes to around 50-55 mph and 2nd gear goes to 100 mph. That is absolutely asinine!