2001 Dodge Ram ABS Kicks on

I have a 2001 2500 Cummins Quad Cab 4X4 and when I come up to a stop the ABS kicks on for no reason. While my mechanic rode with his computer hooked up the wheel speed sensors would go to zero at various times. The left front did it the most but the right front and rear also did it. The computer is not throwing any codes but driving it is getting more and more interesting. Any thoughts would be appreciated as I have replaced the master cylinder and spent a major amount of time and expense working with a good mechanic that is now scratching his head getting ready to go through all of the grounds on the ABS system.