Balance Issue / Vibration

More than likely it's because you don't have the transmission full of fluid yet.
That was my first thought as well, so I let it idle in neutral until fully warmed up, mostly to check for leaks with all the new plumbing in my custom coolers. Shut off, pulled the dipstick, added fluid and restarted a couple times. Had warm fluid flowing all through the system. No leaks, but only got 2 gallons in it. Seems like it should have taken more. I will try it one more time with the new driveshaft installed later this week after I get it from the shop. It definitely has a neutral balance flexplate, B&M-style SFI.

Do you think maybe it will take longer to fill the torque converter?