XRS comes on after 5k miles

the car seems to have come on suddenly after 5 K miles.
it seems to run differently.
i'm wondering if the programming in the control box does this.

i could understand it loosening up a bit but right at 5K its personality
really did change.
the maintenance light came on, i changed the oil and filter i had bought the
previous night. i reset the light as suggested in the owner's manual.
i'm using mobil one full synthetic 5-30 as per the manual.
i don't think the oil change would make the difference.

any thoughts or experience with this?

sammmm