My new PW seems to bounce between 50-70 mph

[mcarey]

The interstate I refer to is concrete. One reason I know the road is causing the bouncing is that the bouncing abruptly goes away at a certain point of the road. That is with both the 1500 and the PW. I'm pretty sure the wheelbase length is matching the segments in the road or something like that, or height variations in the segments of road that the concrete planer didn't take out.

The vibration you describe is different. I wouldn't call the bouncing I'm describing vibration. The bouncing is irritating, and seems to be tied to wheelbase length.

I call that galloping. Happens to me on concrete highways, too.

I've read it's caused by exactly what you are saying as well.