4 and 1/2 quart oil change?

[Axle]

I've only known 5 quarts. I'd be more suspicious of the dipstick being correct.
Do you see any scratch lines in it above the factory full mark? If so, probably at or close to the 5 quart point. Ford (yes, I mean blue oval) had a tsb out in the early 90's for late 80's dipsticks that where stamped wrong. Basically said drain, new filter, fill with 5 quarts and take a hacksaw blade to mark the proper full level.