2000 Ford Explorer Brakes pulsate

Have a 2000 Ford Explorer that when go under 10 mph the ABS system kicks in & releases the brakes then have to push the brake all the way to floor to stop. Kind of feels like when stopping on snow/ice. I've replaced the brakes, ABS pump, emergency brake and roters. Taken to different shops, no computer codes coming up. No engine or ABS lights coming on. One thing noted, if disengage ABS, the breaks are fine; but, the spedometer doesn't work and the engine light comes on showing a rear sensor problem. If reengage ABS, the codes go away & the brake problem comes back. I've been to many different shops, no one can figure out problem.