A veteran Guzzi owner friend of mine, that also owns a Savage swears by ATF...
He says it's right about 13wt... and works real well...
I think it's Honda that recommends it in their manuals...

So, I wouldn't be afraid to try it...

The specifications for a good Dexron III fluid generally show a 7.0 to 7.75 cSt Kinematic Viscosity (at 100 C) and a 40 C viscosity of 35 cSt. Flash points are about 367 F, pour points are -60 F, and sulfur is 2200 ppm with phosphorus being 620 ppm. The SUS viscosities are 17,500 cP at -40 F and 1,350 SUS for -10 F.

Here is the chemistry for an ATF such as Dexron III:
(Average additive concentration by wt.% taken from seven (7) different additive packages)

Phosphorous - 0.3% AW additive
Zinc - 0.23% AW additive, anti-oxidant as ZDDP
Nitrogen - 0.9% AW additive
Boron - 0.16% Detergent and AW additive
Calcium - 0.05% Detergent/Dispersant, tbn base chemistry
Magnesium - 0.05% Detergent and base chemistry
Sulfur - 0.55% FM and AW
Barium - various% used as particlate control

The calcium and magnesium need not be as strong in ATF as in IC engines, because these dispersant/detergents don't have to work so hard removing (cleaning) the carbonaceous deposits and sludge created by blowby.

DexVI is also much improved in the area of shear stability.

For a mineral-based Dexron III, the fluid may start out at 7.5 cST and shear down to 4.5 cSt within 30k miles.

For DexronVI, the fluid starts out at 6.0 cSt and may shear down to say 5.7 cSt.

The reason for the improved shear stability is due to two pieces of chemistry:

1. Some formulators use improved and highly stable VII polymers;
2. others use the new HM polymer esters not considered as VII chemistry.