Computer problem
1994 Chevy Cheyenne V8 Two Wheel Drive Automatic 192650 miles
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I was recently passing one of those speed signs (electronic) that tell you how fast you are traveling. The sign told me I was going 25 mph while my speedometer told me I was going 30 mph. I have not put any bigger tires on the truck than the original size. What could be the problem?

not properly calibrated radar detector.