code: 72 on a 95 chevy 1500

i have a 1995 chevy silverado 1500 4wd auto trans. 350 mileage 250000 milage on trans about 140000. i have had this truck lifted for about 2 years and havent had any problems. but recently the speedometer has started to jump around and it feels like its shifts from overdrive or third back to second gear and when this happens the ABS light comes on. i have had it scanned and it pulls code 72 speed sensor output, or output speed sensor im not sure how it was worded. I have replaced the speed sensor, tone ring, output shaft bushing and seal, the pig tail on the sensor wiring, the front abs wheel speed sensors and the pcm. I am hoping you might be able to tell me what the problem is thanks