where is the oil pressure sender located?

You may need a oil pump I would have that checked out better safe than sorry

The oil pressure sensor is on the engine block at the rear between the cylinder heads. Another cause of low or bad oil pressure readings is the oil gauge itself, that's a common problem on the 03-06 Silverados. Each gauge has a motor that controls it's needle movement and when the motor goes out the gauge will either stick, jump around or die all together. If you'd like to learn more about the problem and how to get it fixed please visit our site at www.drspeedometer.com Thanks, Fred Dr.Speedometer