Thanks guys- I worry about the worst and am very doom and gloom, lol.

Doug, you're right. The rearend feels perfect with everything in the air, no slop, no runout, and no vertical/horizontal play in the pinion at all. Backlash is ok, no signs of heat either. It definitely leaked a bit from the pinion seal but was dry this morning after I wiped it off yesterday.

Clark and Cab- It has a helical style Strange s-trac in it, have driven the Eaton version in other street cars and it typically doesn't bind up like this. It's perfect launching in a straight line and is unlocked like I'd expect at light throttle. I did a bunch of tight turns in both directions in parking lots at various throttle positions and it feels fine, the diff itself is ok.

Investigating further, it only happens on off camber, tight left turns. Looking at the tire clearance, it appears to be touching the wheel lips in those maneuvers and that's what I was feeling in the car. There are fresh rubber marks on the front edge of the wheel lip and a corresponding mark on the tire. It used to not touch there but the combination of new springs, the slightly taller perch to tube distance with the dana, and the angle shims tilting the diff forward some have reduced the wheel clearance to the point where it must hit if the body rolls enough.

For the vibration, this is the first time I've had it above 75 mph with the pinion angle shims. I checked angle again, it's now at -4.3* compared to the trans. Calvert suggested anywhere from -2 to -4, I am going to change the shims from 4* to 2* to see if the vibration gets better. Beyond that I'm out of ideas. It felt OK under power but 90 mph coasting or lighter loads it vibrates and I think that is indicating driveline angles. I'll also check the trans mount.

Have one more Summit order showing up on Wednesday, including the shims, a new pinion seal, nut and washer, plus backup ignition parts. Really hope reducing the pinion angle fixes it!