Speedometer is reading 30mph over all the time

replace the speed sensor and have a shop properly test the MPH

These 03-06 Silverados are bad about this kind of problem, it's caused by failing stepper motors inside the instrument cluster. 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