89 K3500 7.4 th400 with abs, just replaced the module when I got the truck, abs does seem to be working. The problem is after the abs kicks on the truck will start stumbling at idle, it doesn't stall but sounds like it wants to. After I go at normal speed for a few minutes(anywhere from 30mph on up) it goes away. The truck runs/idles fine other than that, just had a tune up. Any ideas?