This comes under the heading "for what it's worth..."
The vehicle is a 2006 with 124,000 miles; last week, I filled
the tank and after driving away got the yellow caution warning
with the script 'check fuel cap'. It appeared to be tight, but I
removed it and tightened it once again. Warning light stayed on.

Purchased a new cap thru Nalley; noticed the new rubber gasket
was tan in color vs the original cap with gray colored rubber. No idea
the significance of the color change. The light and message stayed
on for a few days (probably about 10 'starts' later) then went off
along with the message. Perhaps the computer finally 'recognized'
the new cap.

Cliff