I know this topic was brought up a few months ago and I don't think anyone actually posted the reason for the change between the old Ford 5w20 spec WSS-M2C153-H and the new Ford 5w20 spec WSS-M2C930-A. The old spec required the oil to pass a double length Sequence IIIF test (160 hours) with a max vis increase of 200%. (The standard Seq IIIF for GF3 was 80 hours with 275% max vis increase.) For GF4 the Sequence IIIG test replaced IIIF and it requires 100 hours with a max vis increase of 150%. As you can see, the IIIG is quite a bit more stringent than the old IIIF. Evidently Ford concluded that any oil that can meet the IIIG requirements would in fact pass their old double length IIIF 200% max vis requirement.