1995 Pontiac Transport Traction Control

I have the TCS light coming on on the dashboard. I have a scanner and there are no error codes coming up. I can however read all 4 wheel speeds when driving. The TCS light only comes on once I take a drive. If I leave the vehicle idling there is no fault only when I pull away and go over 5 miles and hour does the light come on. All the other lights stay off. I have replaced both the front wheel hubs/speed sensors and the rear hubs/speed sensors. I have still however got the light coming on and no error code for a reason. Also if I go to switch the traction control off it still happens and once the TCS light comes on my control switch for the traction control is useless.
Do you have any ideas as to where I can look now because I no longer know what to do and I have already spent a fortune on this vehicle by just replacing the hubs.
My worry is that I can read all 4 wheel speeds and there is no difference between them.
Thanks
Wayne