Looking at the data sheets of PU & PUP 5W-20, the most notable changes are the VI increased from 154 to 164 and the Noack V declined from 5.0 to 10.5 (that's not good)
Pennzoil also had a data sheet PU 0W-20 and it never made it to the shelves. Now they have one for PUP 0W-20 but I'm not holding my breath.