Recently my 90 Accord LX (212K miles) was feeling like something was loose in the steering. Once closely inspected, the lower ball joint on the right side was a little loose. So, I replaced both lower ball joints in the front with ones from Checker auto (they were Mcquay-Norris brand). Well, that was a pain to change, but I got it all done in a couple days. Now, when I'm at highway speeds, the steering seems like it is really light - in other words, it goes straight just fine, but it feels like any minor steering makes the car want to swerve). I can control it, but it does not feel safe. I raised the car back up and checked both sides - everything feels nice and tight. I'm trying to figure out what could cause this - my guesses are:

1. the old ball joints were a lot stiffer since they were old, and the new ones just move more easily, hence the light steering

2. alignment is off (but the car doesn't pull to either side, so it seems unlikely)

3. shocks/struts worn (although it seems OK when I press down on each corner - the car comes back to a resting position within a bounce or two)

4. power steering malfunction - it is supposed to assist fully when the car is parked, but less and less the faster you go. Maybe it is malfunctioning and is assisting at highway speeds.

Does anyone have any suggestions on what might be the problem? Thanks in advance.