Vibration or Shudder at full steering lock

Willhound

I plan on having my BIII drive checked out and probably re-built this winter. Ever since we've owned the boat (this spring) I've noticed a vibration or shudder from somewhere in the back end, feels obviously drive related. But only at near or full steering lock at each side. Strong enough that you can hear it and feel it in the wheel, not so bad that the whole boat shakes. At least, not much. 
Worn drive shaft or gimbal bearing? Or is it just that at full lock I'm stressing the u-joint? At all other points in between and at any speed everything is fine the rest of the time. It hasn't seemed to get any worse as the season has gone on, with about 60 hours running time.
Just like to get some thoughts for some preventative maintenance and what to watch for before it maybe turns into something more drastic.

rasbury

 Well, no expert here but the two boats I have owned that were I/O did not seem to like a full turn of the wheel. Now, maybe they both had bad bearings, not sure. I just replaced mine on the 270 an anxious to see how it does in the water and I had the coupler replaced a year ago July so perhaps I will have more knowledge, assuming I still have a boat after Erma!