I have a 2003 2500 5.9. The overdrive was clunking when shifting into overdrive under load with a 10,000 lb trailer with two horses mostly going uphill. I had the transmission looked at and there was a bad bearing that needed replacing and I had a rebuild kit done as well since it was already opened. But was told the overdrive unit was OK. The clunking has returned. I was told it was the overdrive plates chattering because they couldn't handle the shift at the lower rpms with the load. When hauling horses we tend to accelerate and brake slowly. I was told to turn off the Overdrive when hauling below 50 MPH then turn it on when I reached cruising speed. Does this sound right or do I have a bad overdrive unit?