I own a 96 4x4 Blazer with a 4.3 V6. I recently noticed that once in awhile when I am cranking the engine the speedometer will jump up and down. It will also sometimes jump all the way up to 40 when the engine first fires up. Is this normal or what may cause this to happen?

 

No it's not normal. It's probably the stepper motor for the speedometer going out.