Amsoil did list MTG as the recommend fluid, however, it's been removed since Ford was having a lot of issues with the MT-82. Amsoil didn't want the blame for a fault with Getrag/Ford.
In Michigan, I'd be more inclined to use Amsoil Synchromesh. It's a lighter viscosity than MTG that is more forgiving in your cooler northern climate. Red Line MTL is also a lighter viscosity.
Some members of S197 forums have also reported good results with Royal Purple Max Gear 75W-90. I would only use this in warmer climates myself.
Been digging up some VOA's (Virgin Oil Analysis) on Red Line MTL, GM Synchromesh, and Amsoil MTF (synchromesh).
They look darn close to me, very hard to tell the difference in additive content. The major difference will be in areas a VOA will not detect, base stock type.
Red Line MTL - TAN and Oxidation levels suggest Esters (group IV) base stocks
GM Synchromesh - it has one heck of a Magnesium and ZDDP ppm boost.