Driveshaft carrier bearing failing ?

[Dave C]

I just returned from a trip to Florida and Georgia in the 87 5ktq. 
The monsoon season was in full swing and I encountered a problem
during hi-speed driving on roads with accumulated water ... the car
would develop a violent shudder like an out of balance washing
machine.  It seemed to be coming from under the middle of the car. 
Taking my foot off the accelerator or shifting in to neutral made no
difference.  I'd coast to a stop, wait briefly, then go on and all
would be normal for awhile.  Wet roads and normal rain
were no problem, torrential downpours with inch deep water on the road
would bring it on.

My theory is that water was drenching the center carrier bearing which
would begin to bind.  I'm not sure this makes sense, but it's the only
thing I've come up with so far.  I jacked up the car and the bearing
looks the same as it always did.  I greased the U-joint within the
past month.

There are 140k miles on the car and as far as I know there has never
been any work done on the driveshaft.

Do I need ...
New carrier bearing?
U-joint?
Driveshaft alignment? 
Move to Arizona?
- -
Dave C.