suzooka,
I had the same problems you are talking about. My drz 400E wandered when the terrain was rough, head shake at race speed, bottomed easy, the rebound was kicking me all the time. It was like riding a pogo stick through the woods.
I sent it to MX-Tech. Very costly but what a difference. The bike stopped wandering, I am now able to slam obstacles without fear. I almost sold my bike but after the revalve my speed increase dramatically because I was not fighting the bike anymore. It still bottoms on real hard hits but how can you stop a 290 lb bike from doing that? I am very happy with the results. Jeremy was a pleasure to deal with but depending on the time of year it can take a while. It took 3 weeks to get mine back but that was in the early spring 2001. I can promise a night and day difference going with Jeremy.
The only adjustment I made was one click harder on the rebound and thats all I've ever done.
You won't be dissappointed!!!
later,
Mike