I have to agree with Markwb and others, the oil sending unit has failed (mine did the same way).
And the fuel sensor needs inspection.

Found the access panel for the fuel tank. Can someone tell me how to test the fuel level sender? Also, where is the oil pressure sender located? Is it hard to change? thanks

Oil pressure sender is on rear/passenger side of engine (in front of firewall) above the oil filter. Been a while since I changed mine... seems like it takes about a 7/8" or 1" socket to remove and install. Should be able to see the wire and the connector plugged into sensor.

Fuel level sensor / float sub assembly is part of the fuel pump assembly which is inside the gas tank. If you remove the access panel in the trunk you will see a circular item with the fuel lines and wires. After removing fuel lines and electrical connection, entire fuel pump and sender assembly comes out by rotating (seems like 1/8 to 1/4 turn) and lifting out. If you buy a new sensor assembly should come with intallation instructions. Also be aware you may need new gasket if you remove for testing.

Not sure how to test... you can read some resistance if you can locate proper points but need to be careful. If you are electrically inclined, the sender is a potentiometer... has lots of wires coiled closely with a finger that moves along these changing resistance of the circuit. When I removed mine, I could see where the fingers had worn through and were not making contact on the coiled wires any more.

Good luck... be careful with gas.

You can't buy just the fuel sender alone, you have to buy the whole pump assembly with it. Very expensive from GM.
Easy to change though. You will need to siphon the fuel out of the fuel pump canister before pulling it out because you have to tip it sideways to remove from the trunk floor opening. The seal is reuseable.