The speedometer when awry on this truck yesterday. It froze at 65 mph while
driving. Then after a few stops it began to wander from 50 to 120 mph. Now
it generally stops at between 35 and 55 mph with the vehicle stopped, and
freezes there when the engine is turned off, without returning to zero.
This is one of the "dial" type speedometers, and all the other
instruments -- tachometer, engine instruments, odometer -- work fine. This
happened on a cross country trip last September, but it fixed itself after a
day or so.

Does anyone know where the speedometer sending unit is located? I assume it
is on the transmission, but is it top or bottom, left side or right side?

This sounds like a broken wire/ground problem to me, but any ideas would be
appeciated before I take it to the Chevy house. Thanks in advance.

-John Banister

This is a situation that the GM trucks of this vintage are notorious for.
It's the stepper motor in the cluster thats the issue, not the speed sensor.
GM has a goodwill warranty replacement program. My '04 Avalanche speedo
would do the same thing...it was 6000 miles off warranty when it started.
Called my local GM service manager and he called GM's area rep and the
entire cluster was replaced for free. Local dealer said they have seen
dozens like this on the entire line of '01 to '06 full size truck and SUVs.
Dealer said the cost would be in the $700Cdn range to replace the cluster
with a rebuilt GM unit. 20 min. replace the cluster. So I'd be talking to my
service manager if I were you.