Manual Trans Oil Question

The recommendations are all over the place, even from official sources.

Ford had recommended Mercon V
Tremec has recommended DexIII/Mercon and GM Syncromesh
Tremec's service Manual manual recommends Mobil 1 ATF.

I ran the D3/mercon in my 2003GT. The factory fill, IIRC, was synthetic. The early T-3650 was plagued by notchy shifts so an early recommendation was to use non-Syn trans fluid as a way of mitigating that. Later, 2005+ T-3650's don't have that issue and the fluid recommendation changed for those, which muddies the waters when searching for info as to what to use. I think any of the above 3-4 fluids will be fine

I would not use the Mercon LV