Has Anyone Experienced this?: Check Engine Oil Level

[Critical Drew]

Several Months ago My 03' 4.4i would intermittently put up the message "check engine oil level" on the Info Center After shutting the car off. I checked the oil several times when this happened to be safe. It was always fine. Eventually this happened almost everytime I shut down
I determined that the sensor must be bad.

When I did a full oil/ Filter change last week I also replaced this sensor which is on the bottom of the sump.

I took the car to the Stealership and they charged me about $320 for a diagnostic and reflashing a software update to the info center.
Strangely the warning is now occurring several minutes into most drives. I added 8.5 qts. of new oil at the change and the dipstick reads normal.

I called the dealer back, but they have no ideas (of course).

Does anybody have an understanding of this system? Or has anybody been through this? And what was the fix?

Thanks