Speedometer reads way too high.
 

My 04 2500HD recently started reading way too high on the speedometer. The rest of the instrument cluster functions fine. Is this a cluster issue or a sensor issue? Thanks.

Re: Speedometer reads way too high.
 

First, may sound dumb, but did you change tires at all?

Other than that it could be the cluster or the electronic sensor/adapter (not sure what they call it) on the transmission.

Re: Speedometer reads way too high.
 

This problem occurred months after the tires were swapped, and while a speedometer read different according to tire size, these tires are not really large enough to matter or cause that high of a reading.

The speedometer "fixed" itself yesterday, so I'll ignore for now. The cluster has been doing other strange things occasionally too. I'll probably have to replace it eventually. Thanks, anyway.

Re: Speedometer reads way too high.
 

You can get the cluster repaired fairly easily and it's not that expensive. If you try to fix it yourself and make a mess it gets exponentially more expensive.
The most common cluster issues are failing stepper motors along with SMT resistors that develop cracks in the solder joints.
A novice can re-flow the cracked solder on the resistor groups with a decent temp controlled soldering iron.
Look at the jeffescortlx YouTube channel for cluster disassembly howto and what resistors you want to re-flow.
One of my pet peeves is the DIY guys that leave fingerprints on the printed gauge face because they aren't careful to keep their dirty paddies off of it. Cleaning attempts usually make it worse.
Another pet peeve is the guys that get ham handed with the plastic clips that hold the cluster together.

My other pet peeve is the ham handed attempts at stepper motor replacement that result in ripped out plate thru holes and torn traces. The steppers should be handled by someone with experience. I've seen the aftermath of amateur replacement attempts. Sometimes they can be salvaged and other times they are a total loss. The plate thru holes in these boards are fairly fragile so I wouldn't recommend a DIY guy start on these replacing the steppers. A novice can get in real trouble darn quick desoldering with braid and-or a plunger pump. Fragile stuff like this should be removed with decent vacuum pump desoldering setup and some experience in setting the temperature to avoid damaging the board.

Self healing electrical issues point to wiring problems or cracked solder joints in the cluster.

You may find the VSS is at fault but you need to diagnose it or you'll be needlessly replacing parts.
Before you load the parts cannon you may want to examine the connection to the VSS on the transmission or transfer case tailhousing. Check for green or white corrosion and other evidence of water damaged connections. You may want to track down the other ends of the VSS wires and make sure your favorite rodent hasn't been chewing the harness.

You can securely lift and support the vehicle, backprobe the sensor connector, and watch the waveform on an automotive Oscilloscope with the drivetrain turning. The four and eight channel 10-50mhz USB scopes that plug into a laptop have come way down in price.
If you drive the truck over a gaggle of nuns or kill yourself because you didn't properly support it it's on you.

If you need to look at the output from several sensors more channels are nice to have. The other thing to keep in mind is more bandwidth isn't better just more expensive. The scope in the Snap-On Vantage is around 3mhz and that's plenty for most if not all tasks.

PicoScope has pretty decent software but it's more expensive. Toyota and Nissan dealership shops among others use Picoscopes in their service departments.
Hantek 1008C works OK but the Hantek software is not as easy to setup and is reputed to be glitchy.
You get what you pay for. The $100 Hantek 1008C will do the job but the $900 Pico is a lot nicer.