Front and rear differential change 3.73 to a 4.10

[Lyradhunter]

I have a 2004 Avalanche and recently changed out my front and rear differentials with lower ratios to a 4:10. I bought complete axle assemblies from a wrecked vehicle and installed them myself. The truck runs fine, everything works, but the speedometer is not accurate any more, knew that would happen. I purchased and aftermarket tuner that could adjust for differential changes, it asked what gear ratios vehicle had and I put in the 4:10. Drove my truck and in 1/2 mile my service brake light came on, it would reset after shutting vehicle off, but come back on in 1/2 mile.   My understanding of how this system works is that there are two speed sensors for the front wheels and one in the transmission for the rear wheels. The ABS system uses these sensors to detect if slipping of wheels is occurring, so by changing the gear ratios it is changing the relation of the sensor because the engine now has to spin more to go the same distance, but the front sensors are not affected by this. I took the aftermarket tuner back. 

Could I reflash the pcm with a vin number from the same year truck only with the towing option which has the 4:10 ratios?

I had an 2001 Silverado that had an engine replaced, original engine had an EGR valve the replacement did not, so the check engine light was always on. I was able to reflash the VIN number to that of the same vehicle which did not have and EGR valve and my check engine light went out.