Jeakle

Yes. At 30-some items already...hate to image the current system when I have 100+

To copy everyone else, "MORE STRUTS!" Err...ok, maybe not more, but better placement will help a lot. Two struts connecting each rocket on the the lowest stage, one connecting top-to-top & one connecting bottom-to-bottom. All of those higher struts are, IMO, are pretty poorly placed. I suggest, removing those I-beams and just placing one strut connecting the top of each tank to the mid-to-top of the higher one. You can do a similar setup to stabilize the cargo if need be. Struts from the middle of the mid-stage to the base of the cargo. Also, disable the gimble on the outside rockets, use the central one to steer with. You lose turning power, but gain stability. As the ASAS can cause some pretty crazy wobble if it has too much turning capability.

On a similar note, those interstage fairings act as adapters of a sort. But what seems to be missing, and would be nice to have is some basic adapters. Say a 3.75-to-2.5 adapter.