2006 E 450 6.8 ltre

I have a e 450 that has multiple codes that deal with throttle actuator forced closed and stuck open. I replaced Throttle position sensor and actuator or throttle motor according to part place. Vehicle still will lose throttle once speed is drop below 20 mile per hour. Like losing communication. Throttle pedal sensor reads fine on data stream. Any ideas of what could cause this problem. I ma going to look one more time. maybe I missed something.:banghead: