Swapped from a 231 to 242. Now vibs.

[glennv]

I wanted selectrac on my dd so I install the new 242 and ended up with vibs at 65mph+. I have a 2" lift and had no vibs with the 231 and a t-case drop. I installed the 242 with the t-case drop. The drop is about .75 inches. Should I go lower on the drop or could the t-case drop be the source of the vibs since the 242 is a bit longer?
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[Achmed]

Try removing the TC drop and see what happens to the vibes.

 

[Dundy]

yea x2

 

[The Smiths]

x3

Also was there still movement in slip with the existing prop?