GMC Repair: speedo intermittant on 03 duramax/allison, gm trucks, stock truck

Question
2003 GMC K2500HD w/ duramax/allison. The speedometer has recently started to read low, below zero or normally. The failure seems to be to start within 10min of running the vehicle. When in failure mod engine/xmission performance is normal, the cruise control and odometer work normally so I conclude that the vehicle speed sender is ok and the ecm is processing the data. I conclude that: 1. the speedo drive transistor in the ecm is bad, or 2. there is a thermo-intermittant in the ecm or 3. the speedo readout itself is defective. I have removed the i/p cluster for inspection. The speedo is free to rotate. No error codes are present. The wiring harnesses appear to be in good shape and damage free. The GM shop manual isn't helpful for this problem. Questions: 1. What do you think? 2. What does the vehicle speed signal look like? A varying voltage or current? 3. I am concluding that the ecm has a thermo-intermittant in the speedo drive signal. What do I need to do to reprogram a replacement ecm to make my stock truck?
Thanks

Answer
Hi
Your #3 is correct.
These vehicles (GM Trucks/full size SUV's) have a SERIOUS problem with the clusters.
You will need to replace the cluster, and also have it programmed by your local dealership.
As stated, this is a VERY COMMON problem.
I do not know the mileage on your vehicle, but you MAY be able to get it warrantied since it is so common.
Just advice from experience.
Good Luck
Pawl