Okay, I have yet to figure this out. At 60mph I get a horrible vibration that doesn't go away as speed progresses. I've checked pinion angle, driveshaft balance, wheel/tire balance, lift bar adjustments, u-joints, etc. & it's still exactly the same. Any suggestions or ideas before I take it to a frame shop? The car was in an accident over the winter before I bought it, I had a shop install a new front crossmember & control arms (guy hit a steel construction road plate) but vibration is coming through the rear (feels like a bad u-joint). Plus my new Lakewood lift bars are cracking at the axle mounting brackets! Maybe related, I don't know but I'm at my wits end here! Thanks!

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'91 Z28 1LE; 355, Sportsman II heads, Edelbrock TPI w/ 58mm TB, Tremec TKO 5-speed, 3.73's & much, much more

so you've taken the driveshaft and had it rebalanced and replaced the ujoints? sometimes a visual inspection won't cut it. just a thought.

was it vibrating before you put the lift bars on?