Cntrysthbst, interesting problem. If it was engine related I doubt you would feel it everywhere but I could be wrong. If it were tire or rolling gear related seems like you would feel it all the time. Hmmm, you have ruled out just about everything. How about the driveshafts, differential and tranny assembly? have you had any work done in those areas? How long has it been doing this, and anything else feel different than before? I don't get the intermittent part but does it do this everytime you drive it? Does the incident seem to be occurring ?