Allison Indianapolis plant sells to OEMs, makes 1000 series (same used by Chevy/GMC HD), 3000 series (MD), 4000 series (HD), military, off highway, and hybrid bus.
Allison Baltimore plant makes same 1000 series tranny exclusively for GM Truck plants and also future dual mode hybrid production.
GM could trade Allison for Chrysler. Daimler could use ZF for manuals and Allison for automatics.