@craig- I hate to be the 1 to suggest this, but if tire pressure isn't too high, greasing the beam and removing/changing shock absorbers doesn't find the problem there are 2 things to check.
First check that the ball joints were properly oriented when they were installed- 
The ball joints need to be correctly aligned to function properly. If 1 or more aren't the front will ride rough and the ball joint itself will self destruct faster than normal- how fast I don't know, but they all need to be in the same plane as the trailing arm movement. You can see the damage that's been caused below
2nd- The beam itself could be bent. If it was brand new when installed in the car then it'll be fine but if it came out of a donor car (and that car was sold for parts because it rear ended something) it's something to check. If it's bent on 1 side (I've seen just the bottom tube tweaked and it doesn't take much) the trailing arms will bind when they move and make the car ride rough.
Hope this helps. Al
