I've got a 2010 9770 that started making noise whenever the Pro Drive shifted into the high side.  It doesn't sound like gears grinding, but it makes enough noise that I don't want to run it that way very long.  As long as I stay under 4.5 mph it doesn't make any unusual noise.  About the same time that the Pro Drive started acting up, I would lose power steering randomly while combining corn.  Going straight wasn't a big deal, but following contours was a problem.  The steering wheel would turn very hard with very little movement at the rear tires.  I had the John Deere dealer send a tech out to the field to look at it.  He put a gauge on the appropriate port and said I had the correct pressure.  It appeared to behave appropriately as I turned the steering wheel in either direction, but the wheels wouldn't turn, then with no explanation, steering would come back and work fine.  I had the tech listen to the noise the Pro Drive was making and he had no idea what could cause that.  He had very little experience with the Pro Drive transmission, so he was honest about that.  He checked all the final drive couplers but found none that were bad.  We had a few hundred acres of corn that were in fields that would require no road travel, so I elected to finish combining those fields and the dealer found a JD 680 that I could rent to finish the farms that I had to travel very far to finish.  I discovered while combining the last fields with the 9770 that when the power steering quit, if I would bounce the steering wheel lightly when the power steering disappeared, that it would come back.  I'm not very confident that I would be comfortable doing that at road speed, but since I was limited to 4.5 mph, it wasn't a huge deal.  My son worked on the wheat run with S&L  a few years ago and was in contact with the guy that took it over when they retired.  He suggested that the coupler that drove the Pro Drive was a common issue.  When we got done we pulled the hydraulic drive motor that drives the transmission and the coupler and shafts look fine.  I've been looking at JDparts.com and it appears that there are clutch packs in the Pro Drive.  Does anybody have any experience with this?  I do most of my own mechanical work, and I have no problem paying for things that I don't know how to do, but I don't want to pay the going shop rate to educate someone else.  It also appears to me that the power steering and the Pro Drive are on separate pumps and hydraulic systems.  Are the problems related or is it just bad luck to have them happen at the same time?