GM originally specced Dex lll in their T56 manual transmissions. When Dex III was no longer being made/licensed GM changed my trans fluid to their own "upgraded" version of ATF - called "manual transmission and transfer case fluid....GM #88861800). They still make it too though it costs a bit. Instead go with the same stuff from ACDelco Manual Transmission Fluid 88861800 or ACDelco10-4033.
For Fords they left ATF Dex III behind and upgraded all their older transmissions to Mercon V around 2000-2001....basically a semi-synthetic ATF Dex III with a slightly better add package. But I'd bet they are nearly identical. For any Dex III application I'd use the Mercon V's.....SuperTech has Ford approval on their Merc V. Same stuff as Dex III, same viscosity, just a better product, that shears less than the conventional grades.
And the Mobil 1 ATF is a good synthetic Dex III with a much improved add package. Same for the Amsoil ATF's and Redline D4 ATF. All of them are Dex III viscosity, with improved add packages.