staged70

So when I changed my 03 GMC ECM back to an original equipped item I had it re flashed. Then the tow haul feature stopped working and if you turn the fan speed switch to 3, 4 or 5 it runs very bad the volt gauge drops to 10 volts and the truck will eventually die. The switch tested good, fan motor is good , exciter wire is working as it should. Alternator is working as it should. All this seems to have started with a water pump failure it covered the engine bay.
. New MAF and PCM installed grounds checked and cleaned. The truck had a ECM out of a Escalade with a non factory tune, showing it as a 1/2 ton and having the wrong VIN in it. Dealer tried to re flash and got the truck in a security lock condition. I had to tow it away from the local GMC dealer and fight so I would not have to pay them for the re flash and 1 hour of diagnostic time. It ran in and was towed out so I wasn't going to pay them for breaking the truck.
I took it to an authorized shop for the re flash. It has been back to them but still no luck on the fan switch. The shop working on the truck seems lost and I do not have the training or the tools to do the diagnostic work.

staged70

No info on here ? I thought this was the place to get a lead on where to look