TJ shimmy... Its the Harmonics between 38-42 MPh we all have it to one extent or another. Mine is better since I recently replaced My tires. But, I can still feel it slightly if conditions are just right. Guys have spent thousands of dollars replacing parts and Not cured the issue. I have chosen to leave well enough alone, It's inherent to the beast and the straight axle frontend. As long as it dosent become full blown death wobble I'm not gonna fix it cause it aint broke. JMHO tho. probably lots of opinions on what you should replace and why though.