I have a XR4040H. I've had problems with regen and getting stuck in limp mode. The mechanics still can't figure out a solution yet, two years later. That being said, the dealer (RCO Tractor) been awesome about trying to get things fixed. The tractor is there right now, as the bumper to bumper warranty is expiring soon, and their tryingto get things figured out before the end.
But, after two years with the Xr4040H, I found that I need something bigger and stronger with a cab, lol. So I'm probably going to trade this one in for a XU6168CPS, depending on price of course.