Hope you don't mind I split your question off into a new thread.
FYI:
http://www.evdl.org/docs/force1994.pdf
The Solectria cars aren't run-of-the-mill conversions. They're commercially produced from brand new "gliders" bought from GM. (Which is why this car has less than 5k miles on it.)
If the tech in this earlier model is anything like the later ones that I've driven, it's a very slick EV: AC drive, which is both more efficient and equipped with regen. Sufficient power for highway use ~60 mph should be no problem.
There's a Yahoo group dedicated to the car, so you would have excellent support from the community of owners if you need it.
I'm not sure what the battery pack would cost to replace though. Not up on battery types/prices. Maybe someone else could chime in.
If I had the money and wanted to buy rather than build an EV, I'd look for a Force.