I have some typical and not so typical electronic problems.

Tire Pressure Low Warning, even though tires are fine, actually overinflated.

CHANGE OIL NOW, oil has 200 miles on it.

thats it for the DIC.

There is a security light that comes on sometimes, at random, I'm not sure what it means because the car starts up everytime and the alarm and locks work fine. It is intermittent, It seems to come on after the car has been on the road for 5 minutes or so, sometimes it never comes on, but when it does it will not go out until I restart the car. There is NO message on the dic such as "service security system" or anything like that. Where are the grounds for the variuos security features?

Would a scantool be able to show the reason for the light?

What about the ground for the fuel sender, is it under the carpet somewhere?

I don't think a ground wire would cause "Tire Pressure" and "Change Oil" on the DIC. When you inflate your tires and have all 4 of them where they need to be, you should reset the "Tire Pressure" warning message. I don't remember how to reset it, but it'* in your owners manual. Same thing with the "Change Oil" message. The place where you have the oil changed at should reset that message as part of changing the oil process. Otherwise, you will keep getting those messages over and over until they're reset.

As far as the "Security" light, that is weird, but may be tied to your ignition switch possibly going out. Too many variables to look at. Maybe somebody else has better answers?

The first time you hit reset it only disapears from the dlc.
To reset select the change oil now in your dlc by hitting the mode button and then press and hold reset till is says normal. Same for the tires.

Under the rear seat there is a ground lug. Archon has mentioned it a few times lately.

I would start by removing and cleaning all battery cables at all ends and fixing up the grounding lug as suggested by Archon.

I thought I had seen it mentioned, but I have not frequented the 00 forum much until recently.

Anyone know if its possible to troubleshoot the security light with the scantool you get at ADVANCE/Schucks/checker?

Adjust tire pressures to recommended inflation, then press the select button on the DIC until TIRE PRESSURE appears in the display. Press and hold the reset button for at least 5 seconds or more until the tire pressure monitor displays TIRE PRESSURE NORMAL.
As for the GM Oil Life System, press the select button until OIL LIFE appears in the display, then press and hold the reset button, 100% will be displayed.
As for the security light, the only real way to determine what is at fault is to interrogate & retrieve DTC with a Tech II.

Does the spare have a pressure sensor on it?

In regards to the security light (looking like the only problem I dont have a resolution for with the car) The owners manual says nothing about the light. It says if it comes on and stays on for 1 minute after the ignition is turned on there is a problem with the system, it does not mention my problem that I can see. I have another cluster I can swap in too. the alarm works great and I never get a security light initally. Its always after the car warms up.

no, there are no pressure sensors at all.

most scantools can only read powertrain error codes, not chassis, or security/airbags. You need a TECH II to retrieve those unfortunately. :(