The only car I had an issue w/the shimmys was my wagon. Issue for me was at 4000 lbs it did not like the old centerline 3.5" wide rims. Add the Flaming River quick ratio gear box and it was a but pucker ride.
Added 5" rims and put in the factory gear box from my cuda and the car goes down the track like I'm cruising down the highway. Night and day. Some like the quick ratio box but for me it just didnt wk.