Meritor 10 speed whine noise

So I already this company is crap but I have to try and deal with this. I purchased a tranny about 2 months ago. Its a Meritor Rockwell 10 speed. I just purchased the 99 inter 8100 about a year and a half ago. Has cummins m11 also. I purchased a rebuilt tranny and installed it. Took it on an 8 mile test drive to come back and find oil all over the underneath of my truck. Found out after having it towed to my buddys shop that they forgot to put a bolt in near the ouptut shaft and thru most of the oil out. So they ended up sending over another tranny (RMX10125a) to swap out the first one. Got it back about a week and a half ago. With this tranny anytime I am on level grade or a downgrade, the tranny will whine. And it will whine pretty bad when I am between 65 to 70. And putting it in either 4th or 9th, its noisy going in like sloppy gear or something. Also, it had a leaking slave valve on it that I am suppose to be swapping out this weekend. It does not whine when going up a hill though. I spoke to the warranty guy about it and he said it is nothing to be concerned about but I know otherwise. I told him the one that was in there did not make that noise and he just laughed it off. I asked for another tranny, which would be the third one and he said that wont happen unless they thing something major is going on and still may not happen. LOL really. So I am wondering if anyone has an idea if this could be a bearing or what it might be. I just dont want to break down somewhere. I ran from South NJ to Cumberland, MD loaded and then deadheaded back. No problems but whined the whole way. Can get pretty noisy. And I checked my air bag leveling valve and ride height and all seems good.