Oh, if you have the vibration I had, you'll know it. At 75 it felt like the RV was about to shake itself apart and/or the driveshaft was going to come out. I have a lot of experience dealing with driveshaft vibration issues given my hobby (rock crawlers), so I *may* be more sensitive than others to the problem, but I assure you if you have it, there's no mistaking there is something wrong.
My guess is it was not installed correctly so as to keep the front and rear u-joints in the same plane. This is why it shudders on hard take-off. Some angles were off somewhere. I never got under it and looked, I just took it to Ford and said "fix this".
