My guess is that it is now a group 3+/PAO/Ester blend.

Sadly, on most of the 300V Ester Core weights, the VIs and TBNs have gone way down. frown
2000 Z28 1SC 6 speed 170K miles
Red Line 0W-40/Sustina 0W-20 (80/20 mix)
Amsoil EaO 64 filter
Synpower 75W-140/4oz. XL-3
Ravenol MTF-2