Engine/Transmission (1998.5 - 2002) ABS Brake Help Needed

[Sjester]

have a 95 that has rear only ABS. First noted a problem about a week ago. The ABS and brake light came on. I pulled the rear speed sensor, put it on a multimeter and it checked out OK. The speedometer and cruise work fine. Lights reset after the truck is killed but will light again after 10-15 minutes. When they are off, the truck seems to be engaging the anti-lock mechanism at all stops whether harsh or not. You can feel the system dumping pressure. Once the lights come on the brakes work fine because, I suppose, the ABS system is bypassed. I replaced the speed sensor since I've heard of intermittent problems. No change. Wires look fine. Has anyone else experienced this?