E350 front end prob? darts whenever it hits a bump?

I've installed new upper and lower ball joints, tightened bearings, did front end alignment, everything seems tight.... tracks great but jumps left or right nearly every time it hits a bump, then is very difficult to straighten out without overcompensating... repeatedly. This is a 97 Ford E350 with the Triton V10 engine. I noticed two posts (one on each twin I-beam) going horizontally forward that have nothing attached to them: is it possible I'm missing a Component? Any info or direction would help...... Thanks, Mike.