Been fighting this for some time now. Speedometer quit working. Other gauges, ok? Sent cluster in and had it rebuilt, still no speedo or gear indicator (the little line under the PRNDL letters ).

The truck is stuck in tow haul mode, as well. This is a "kind of" intermittent issue, once in a while the truck will start and run completely normal for several miles, then tow-haul kicks in (RPMs jump up) and the speedo and gear indicator bar drops off.

I replaced the Vehicle speed sensor on trans housing, no difference.
AS these two errors sure seem to be related, where do I start looking?

Days later….

Put a new battery in truck…
Got a brand new GM part gear shifter lever (that has the wiring and tow-haul button) and tore shrouds apart and installed it/
Still not right. If I turn ignition on (not starting truck, just lighting it up) the gear indicator works right as I move the lever through gears, and the tow-haul light does cycle.
HOWEVER, when I start the truck, after about five seconds the gear indicator light goes out and tow haul is once again inoperative.
This leads me to believe that there is a "run" wire in the ignition harness that needs to be checked out/

Without a decent wiring diagram I have no idea what to look for. Does anyone here have access to the wiring harness schematic? Info on what to do next?
Oddly the truck drives just fine, apart from being stuck in tow-haul mode (lousy for fuel economy)

 

Scan all modules to see if there are any codes. You may have a communication problem on the data line. Pull up data display for the TCM and monitor vehicle speed to compare with your cluster. I've seen faulty tcm's causing similar problems. It's an easy way to start if u have a scanner.

 

I dug around on Charm.li for a couple of minutes, and found a diagram that shows the Tow/Haul switch on the shifter:

4L60-E/4L65-E/4L70-E Automatic Transmission — 2008 Chevrolet Silverado 1500 2WD V8-4.8L Service Manual | Operation CHARM

It is transmission dependent though, and you don't say which engine or transmission you have. My 2006 WT has the 4.8L engine and the 4L60E, so just went in with that selection. All the diagrams are buried on that site though. Looks to me like the Body Control Module (BCM) is responsible for looking at the switch and lighting the light on the dash. So this could be a BCM issue. This might at least give you a clue of the connectors and wire colors to trace in the wiring harness. Looks like L-BU or light blue?