My '99 Blazer vibrates a bit at 70-80mph seemingly the whole vehicle shakes, but I don't get anything through the steering directly, seems to be the body.

I've not owned it that long, but its in pretty good shape with a lot of invoices for mechanical work dating back to when it was purchased by the original owner.

It's got new wheels and tyres on it, which appear to have been balanced properly.

Any ideas before I just randomly start pulling stuff apart?